I can tell you from experience that a stock B18 head on a B20 block is a big mistake with any intake system. I lived with a B18 big-bore kit for quite a few years, and it's nasty -- a stock B18 will outrun it handily.

I did comment that I know a builder who works with B18 heads on stock-bore B20s (88.9mm), but that's because it permits him to cut away the combustion chambers to match the bores perfectly -- all B20 heads have chambers that are a bit larger than the stock bore (90mm for carb heads and 92mm for injection heads). B18 chambers are 87mm.

(Note here that the B20 big-bore kit uses 92mm bores, which match the injection heads -- these don't have the same problem as the B18 kits.)

You've done well to go to the thinner head gasket, and for reasons on top of just raising compression. Even if the SUs aren't optimum, I think you'll do better with them than with the 32/36.