I had the same problem just a few weeks ago with my 1959 Rochester B carb. The shop replaced the base gasket. But, I have know idea if it is correct now or not. I haven't driven the truck since they did the work as it went straight over to the paint shop again.
My question is, Jon, which one of the gaskets in the link you posted is the "almost correct" gasket?
I am now going to check to see if the power valve port is blocked. Now for the really novice question - Where on the base of the carb will the power valve port be? Front or rear and driver/fender or passenger/valve cover side of the carb?
Thanks!