momxnine,
Thanks so much for being willing to share a bit more about your son and his past academic studies. As we get to the final years of high school, it can be interesting to make sure our students get what they need (and what we want them to have) by the time they graduate!
So as not to confuse our board readers who are coming up through HOD, I'll begin by qualifying my suggestions by saying that these suggestions are unique to your situation (because your son is coming to HOD close to the end of his homeschool journey). With that in mind, based on what you've shared thus far, it sounds like your son could use British Literature to finish out this year (to earn 1/2 credit in Brit. Lit.) and American Literature next year (to earn 1 full credit in Am. Lit.) to finish out the English portion of his transcript (along with grammar and writing) next year.
Our American History guide that will be coming out in installments this fall (beginning in early September) will include a year of American Literature. The guide will be written in real-time, like our current World History Guide, so your son wouldn't be working ahead to finish Am. Lit. but instead would finish when the guide finishes in May. You would receive the plans in installments all throughout the year. If you are thinking that your son would be on a regular schedule for his senior year, then it would be my recommendation that he do the American Literature in that guide (along with the writing that will be scheduled in that guide) for his senior year. You could weigh whether you would also want him to do the Rod and Staff English 8 (first half) which will be scheduled in that guide as well. I think Rod and Staff is oustanding and that students benefit from any time spent with that program prior to graduation, no matter their grammar background, however you would be a better judge of whether your son should do the Rod and Staff portion of plans as a senior (twice weekly) or not.
With the American Literature taken care of in the manner I've shared above that leaves British Literature to cover in the remaining semester he has to devote to literature in his junior year. While it would be fine to do the BJU in the World Geography Guide, there isn't really a ton of British Literature in that particular text (not enough to award credit in Brit. Lit. anyway). Also, since your son has read most of the boy set of books in the World Geography guide, then simply reading the British titles in that set along with the BJU won't help much either. Plus, to cover all of the BJU book in one semester would be daunting (if you added additional Brit. titles, which you would need to do in order to claim Brit. Lit. credit). This is why I am leaning toward having your son do the World History Guide's literature instead but I am thinking he would need to do only the British Lit. titles. This would work since he will not be using the rest of the guide in its ordinary way. To do this, your son would do only the following titles:
Julius Caesar (with audio)
Pearl Maiden
The Story of King Arthur and His Knights
A Man for All Seasons
The Scarlet Pimpernel
* Pilgrim's Progress (see explanation for this title below)
He would follow the plans sequentially to do the books in the order I've listed above. This would give him a formal British Literature study written directly to him and have him reading real books along with it. Even if he has read these titles, to do them along with the plans in our guide would be a nice change of pace and teach a different set of skills then the PACES.
To round out his British Literature credit, I would also have him do the Pilgrim's Progress study that is scheduled once weekly in the World History Guide. I would have him do it twice weekly instead in order to cover the entire book by mid-May of this year. So, Pilgrim's Progress would also be added to his Brit. Lit. list. It is a wonderful study, which would really be of benefit to your son, even if he has already read Pilgrim's Progress. He would just do it according to the plans in our guide.
As far as the witing goes, I would be inclined to have your son do the Essentials in Writing that is scheduled in the World History Guide as well. You could select the units from the EIW that you feel your son most needs this year to finish out his year. I would recommend including the research paper that is done last in EIW, along with any essay types you feel your son has not done previously. Then, the following year, I would recommend doing the writing that will be scheduled in our American History Guide, following the schedule in that guide.
To finish out this year of grammar, you could either do the rest of the ACE PACES and then take a break from grammar, or you could instead do the last half of Rod and Staff English 7 doing it twice weekly to finish out this year. Either would work. Next year, I would be inclined to do the first half of English 8 as it will be scheduled in the American History guide.
As far as science goes, I see that you have a challenge in this area, as you have a semester to fill here and then next year to plan before your son is done. For starters, I would plan to do the chemistry that will be in the new American History Guide next year (even though he has begun Chemistry this year). I will be sharing sneak peeks for this coming up in April or so; however, from what you've shared thus far about chemistry, I do think the Chemistry in that guide would be a great fit for your son. This would also mean he could just follow the plans for that in our American History Guide as written (and you wouldn't need to come up with anything on your own). Since he would be doing the Lit. and writing from that guide his senior year, you would have the guide anyway, making it a good choice to do the Chemistry in that guide too.
With that in mind, you would have one semester to fill this year for science. I would be inclined to do as you suggested and do the 6 pacworks from IPC that deal with physics (and omit the 6 pacworks that deal with chemistry). You could also add the Physics 101 DVDs and then award a 1/2 credit in Introduction to Physics upon completion. Some people, including the publisher of Pacworks, feel that you can award a full credit in Introduction to Physics for completion of what I've mentioned. I feel that is a stretch, but in a pinch, you could possibly list it that way (as long as you clarify that it is an Introduction to Physics rather than a full-blown physics course). This would take care of your science dilemma.
I would lean toward not doing Physics as a lab science, as long as your son has had labs for Physical Science and Biology (and he will have labs through HOD's chemistry). If he hasn't had labs the other years of science, he will need to do the Microphys Sci Kit that we carry along with the PACworks Physics that I mentioned above. We have matched these MicroPhys Sci labs to the Pac Works readings in our World Geography Guide. You could just do the labs that match the Physics Pacworks (and omit the chemistry labs that are scheduled to coordinate with the Chemistry pacworks). However, to do this lab matching you wold need the World Geography guide's plans. This is why I would lean away from doing the physics as a lab-based course unless you truly need the lab credit.
Of course, if you wanted to have your son do the World Religions and Cultures' study in the World Geography Guide, and also are considering having him do the Art of Argument, then it may be worthwhile to have the World Geography guide as well. Since your son is an avid reader, he could perhaps do two days of World Religions... each day to finish it in a semester and do Art of Argument daily. This would give him a 1/2 credit in World Religions and Cultures and a 1/4 up to 1/2 credit in Logic (depending on if he's ever done any other logic type course like the Fallacy Detective). On a sidenote, I wouldn't recommend just reading the World Religion and Culture's books without the HOD plans and the World Religion Notebook, simply due to the fact that there are some areas that need discussion and Biblical references so as not to confuse students as they study other religions. These helps are provided in the guide and the notebook and are essential to the study in my opinion.
These, of course, are just my thoughts as to how you could gain the credits you mentioned by graduation. Feel free to share your thoughts!
Blessings,
Carrie
His writing is not very good since ACE doesn't seem to have much in the way of writing. I was reading an essay that he wrote while doing MFW and it was SO much better than something he just wrote a week ago with the paces. 
I am just so impressed with the unity and integrity of Carrie's selections and instructions, and my son is really blossoming in his ability to use the guide independently along with his growing communication skills. I hope you will find just the right fit for your family.