Well I decided to read the whole thread
How old are those Eddy heads? Where they checked out before bolting them on?
I head Edelbrock heads can be way off. Some shops swear to take apart even a brand new head and check everything. They claim every head has a few things wrong, guilds too tight, valve seats not round, springs weak.
I would pull the heads-if they were not check out ever-and have them look over.
It sounds like valve springs, lifters pumping up. The fact it does it at 4500 when good and hot, could very well be weak valve springs. Maybe the hight was wrong, even a new spring will be weak if the install hight is wrong.
Now yeah, swapping carbs be much quicker and easier, I have a bunch over here in cold snowy Michigan--this stinks, its snowing every day-but I take it you live some where nice
I can't see how a too small of carb could be heat related, thou.