Yea this thread is awesome, I've learned a ton from it. I'm now starting to think the problem is carb related as well, specifically the accelerator circuit getting air in it. Possibly related to a vapor lock problem I'm fighting.
Anyways, turns out the diaphragm in my AR-10 broke right before I had to make a 150 mile trip 3 days ago in 100 degree weather. I went to advance auto parts and bought the only can they had in stock. It's P/N V384Z. With the vac gauge, it appears to start advancing around 5" and fully advances at 13-15". It also has about 20 degrees of advance it it which is way too much, so I had to limit it. This time I used a home made limiter on the back side like the crane one and it worked GREAT. Just had to retard the timing a little to get it back to where it was. Here's a pic. Currently running 34 total + 12 vac.