The really good hotrod stuff for GMC's was produced back in the 1950's when there were thousands of WW II surplus 270's available dirt cheap from the 6X6 military trucks. Diehard stovebolt fans loved them because they were the only engines that could be easily adapted to Chevrolet cars that could almost keep up with the flathead Ford V8's. The 216's and 235's just couldn't make the cut on the dirt tracks. The 270's had lots of torque, so much so that they were still getting wheelspin off the turns when the Fords were halfway down the straightaway. The successful GMC racers eventually learned to gear their cars high and lug them off the turns to minimize the traction loss.
The trick setup on a GMC engine is a 12-port cylinder head- - - -if you can manage to find one. They're scarce and EXPENSIVE! There are lots of go-fast parts out there, but be prepared to mortgage the homestead to buy stuff like pistons- - - -mostly they're special-order custom items with a fairly long wait for delivery, and a high price. Have fun!
Jerry
