Don- Yes, the GMC left the factory with a 336 (actually 337) c.i. Pontiac V8 (a small-bore version of the car's 389). But when I bought the truck someone had swapped in (a better term would be "hacked") a late Pontiac 350. So I built and installed a modified '58 Pontiac engine- which is outwardly identical to the 336 (well, if you ignore the SD Tri-Power intake!). But it's very modern inside- 382 c.i., 9.1:1 C.R., re-designed combustion chambers, hydraulic roller cam, crank trigger ignition, long branch manifolds with 2.5" stainless duals with hand-built copies of the rare GTO option VOE mufflers (switch on the dash makes them straight-through), etc.