First, to comment on your 15:1 idle, I'd ignore that first, with decent overlap on a performance cam, and O2 sensor has no idea what's going on in the chamber and tends to read lean.
Second, I think you need to take this in chunks. Set timing to a standard curve and leave it alone, then move on to the carb problem. I would say that to rule out any ignition curve issue, I'd put that setup at 18 initial, 36 total, all in by 2700, and nothing coming in at idle. For troubleshooting, run without any vacuum advance if equipped for now. That setup should do everything you need it to do and allow you to focus on the carbs
Third, I think you need to get your idle right. Setting the primaries then equally adding idle to the secondaries to get idle speed to where you want it will help you greatly. Adjusting a/f on both carbs as required and resetting idle as required, soetimes youll have to tweak both a couple times as you change secondary plate location This of course assumes you have good carbs and no internal problems
If at that point, the idle isn't good and the vacuum gauge is bouncing, you likely have a tight valve, a valve or two not seating, or a vacuum leak. If the idle is good, and you have issues at WOT, which I suspect you won't, you can start looking at the main and enrichment circuits
I think if you don't do this in order, I think you'll be chasing too many variables.
