What kind of carb spacer would work the best?

This depends totally on the combination, even then no two cars seem to respond the same. I currently run a 1 inch 4-hole phenolic spacer. I've tried 1 inch open, 2 inch open and 2 inch 4-hole. I've always ended up putting the 1 inch 4-hole phenolic back on. My combination just seems to run better with this spacer. Next experiment is going to be a 2 inch Super Sucker which I've been told should help but then again I've heard that before..