Carburetor delima

I would check the condition of the throtle shafts as far as wear with that being equal, understand that they take different intakes or at least a carb. adapter. Everything being equal, I have always like a proper rebuilt Thermo Quad. The 600 if it isn't a Mopar Holley your going to need the extra holley linkage bracket to hook up the throtle cable and trans kick down linkage.