Being a b20E, you'll possibly want to start with it near 10 degrees advanced... They're pretty high compression motors to start with and on todays gas they generally like higher octane and/or lower static advance.

Spark plug gap should be absolutely fine where you have it, I wouldn't mess with it.

If you think the carbs like a rich mixture, then yeah, as others have said, it's probably those little spring valves in the throttle plates. But just to make sure, I'd go through all the little vacuum fittings on the intake manifold and on the carbs(making sure they're connected to something), and make sure you have those two downward facing(towards the exhaust manifold) ports open to the atmosphere.

Go ahead and start with a baseline of around 2.5 turns down, maybe more as your engine should actually want more than mine with the more aggressive cam(well actually, maybe not with the higher compression ratio which would be more efficient), and get the timing to around 10 degrees advanced.

Then work on balancing the idle speed at each carb. I do it by ear, listening to the hiss seperately at each carb. It could be better, and maybe that's why I'm suffering a little bit at the lowest of rpm, but by ear is usually good enough. Some people stick a small tube from their ear to the carb throat to make it a bit more accurate, and then others will use some sort of flow tool. If you have the tool, by all means, go ahead and use it! :)

Once you get it to that point, you should have a pretty darn well running car, that isn't quite tuned to the best, but more than good enough to drive the car around.

And if you don't find some way to get rid of the spring valves in the throttle plates, just run it a little richer. You won't get the best gas mileage necessarily, but it's not going to do much of any harm.
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Kyle - 142, 145, and 244! - Oregon Volvo Tuners?