Vapor lock occurs when the fuel in the carb bowl gets so hot it boils and then it doesn't atomize well. In the old days we used carb insulators and insulated fuel lines going over hot parts of the engine. On Pre-Votec engines there is an exhaust crossover in the intake that heats the area under the carb to prevent carb icing (automotive applications), the gaskets have a restrictor in them to keep it from passing too much heat, if those aren't installed, it could conceivably happen, but this is only on pre-1995 engines, Vortec intakes do not have an exhaust crossover.
How did you determine you have vapor lock?
My old 4.3 has a Quadrajet with the typical thick gasket, never had vapor lock in all the years I have owned it. I did install those restrictors in the intake gaskets when I had the top end of the engine apart.
