The GMC uses a gear drive from the factory, Cloyes did make a suitable performance multi keyway set. Also, the later 250/292 six cylinders that are raced in Comp and other classes have had Jesel belt drives, so I'm sure they can do one for the GMC. You'll just need to decide when making the cam cores if you are going to make the barrel larger, and will you also make the snout larger as well so the cam gear can be made to fit that. The GMC crankshaft only has a snout the same size as a SBC, and many SBC Comp racers upsize the cam journals to BBC and also make their cranks with BBC size snouts as well.
