Intake manifold choices

I don't think the intake swap alone will solve it, after reading. you say the float bowls are not hot to the touch. You may be experiencing fuel percolation in the lines, instead of the carburetor itself. Pay close attention to where the fuel lines run. Are they near any heat sources? Getting the fuel lines away from heat sources will certainly help. Also, a systematic approach will be best, imo. So in other words, more than one thing. Isolating the fuel lines from heat sources. Adding a good fuel return system, with a good return style regulator put in the return line. That way, you're using the regulator as the return orifice, so you can run a return line as big as a sewer pipe. That and a good insulator gasket and or a carburetor heat shield will probably do the trick.......that is IF the problem is fuel percolation. I would verify THAT first.