A GMC 302 head would require 302 pistons because of the combustion chamber configuration. Chevrolet V8 valves -- 1.94 intake, 1.6 exhaust -- can be installed in the 302 head without difficulty. Breathing in the upper rpm range would considerably improve.
In the day, Bill Fisher among others argued that a "small-port" head would be more than adequate for most "street engines." Given the sort of use you envision, you may find that surmise correct. Any improvement in low- and mid-range torque will help. An "RV" cam grind is probably what you want. You probably will not have need for more than 4,000 rpm. i should think that you will not need more than 300 cfm in carburetion. A good two-barrel should be enough. Economy is a concern, and your overdrive should help that, to the extent that it can be helped in a 3/4-ton truck towing a load.
God;'s Peace to you.
d
Inliner #1450
