I've had the same problems as you have....a long long time ago.
have you tried a 1" spacer? there's some spectrum (sp?) company that sells spacers, and they have a neat removable center piece that can be open or a 4 hole spacer....i used the 4 hole spacer on mine (on a 440 with dual plane intake eddy CH4B) and the difference was night and day...i like you tried the like 1/4" eddy thick gasket and still had a heat problem. after i put on this 1" job it totally completely disappeared, and the 4-hole spacer had a second benefit, and just ran much nicer by giving the carb better signal to the barrels...so my off-idle stumble disappeared as well...
also how are your fuel lines routed? do you have a return for a vapor separator as well?
