The first thing that occurs to me is a vacuum leak. Aside from the obvious places
for a vacuum leak, are you sure your crankcase ventilation system is working correctly.

Seeing how nice and shiny your intake manifold is, I'm guessing you had the plug in the plenum out at some point, and the vacuum nipple too. They don't always reseal very nicely, especially if you have used teflon tape around the threads.

Just out of curiosity, what kind of fuel pressure regulator are
you using?
I sincerely hope it's not one of those $25 dollar chrome plated ones with the dial; they seem to have two modes of operation when they are actually working (as opposed to when they are leaking or not passing any fuel at all) that could be described as passing too much fuel and causing your carbs to puke gas, or causing fuel starvation.

You're not stuck with one of those sh*tty Scantech fuel pumps, I hope...

BTW, everything I've suggested here is stuff I fought with when I rebuilt my engine a couple of years ago and put new Mikunis on it; it's amazing how much better the carbs work when all the other stuff isn't messed up...

Are you sure your distributor is working correctly? No problems with the advance etc.

Good Luck

Bill