Actually, that was VWBUSRAT

I'm getting kind of worried about the state of your heads. Your story is starting to sound a lot like Geri Lou's. Bad exhaust leaks, backfiring, stumbling, 009, the whole nine yards.
For the time being, richen it up a bit. Running a little rich isn't gonna tear up your engine any worse than running lean will. You just don't want to push it too far. If there is no lag in acceleration with a 009, or you can see smoke from the exhaust when the throttle is blipped, you are definitely too rich. You should have more of a flat spot in acceleration than a real stumble though. (Well you don't want either, but with a 009 you take what you can get)
Think about scheduling a time to pull Betty's engine and have a look at the heads. Did you ever do that compression test?