Even a "stock" rebuild of a GMC inline six can make a checkbook need CPR. After WW II there were untold thousands of GMC 270's sold for surplus, as a large number of 6X6 military trucks were built on GMC running gear. Sadly, virtually all of them, and most of the 1950's vintage military 302's got sacrificed to the gods of racing- - - -drag racing, dirt tracks, and even a specific class of Bonneville land speed record run that the 302 was used for. The surviving "go fast" stuff is being hoarded by a few GMC enthusiasts, like multi-carb intake manifolds, headers, racing cams, 12 port Wayne heads, and other bits and pieces that are mostly only good for all-out racing.
Fortunately, a basic stock rebuild is all a 302 really needs for a truck the size of yours. It's got plenty of torque to handle the load, and there's not much advantage to going for high RPM horsepower- - - - -that kind of engine build will dramatically shorten the lifespan of the engine! Piston rings, rod and main bearings, gaskets, and other regular rebuilding parts are still available with a little careful shopping. Pistons- - - -they're scarce and expensive, so don't do a re-bore job unless it's an absolute necessity due to taper wear in the cylinders.
The 270's Dad's 34 Ford 3 window coupe was running against on 1/4 mile dirt tracks in the early 1950's had plenty of torque, but not enough traction- - - - -he said his car would be halfway down the straight before they could get hooked up coming off the turns!
Jerry
