I agree with you that the heat transferred by the aluminum foil cover of the silencer pad is going to be small. I'm still inclined to install this pad, but will probably leave the crossover unblocked, unless others have additional insight.
My GTX has its factory fuel lines to and from the gas tank, all per original. As long as it takes to start up (~ 20 seconds), I'm thinking the return line works too well, perhaps draining fuel from the fuel pump. Anyone seen that problem & could it happen without a hole or leak in the pump diaphram? It doesn't seem to me it should take that long for gas to flow from the pump to the carb if the fuel pump is already full. I suppose I could tell by breaking open the fuel lines after the car has set a few hours.