There is another thing I noticed between the GMC and the Chevrolet H-M Flywheels.
This
Picture of the GMC flywheel, shows a rubber crankshaft seal.
This
Picture of the Chevrolet flywheel, shows no oil seal groove for a rubber oil seal at crankshaft.
I think I read somewhere Chevrolet used a paper gasket at the crankshaft. Not sure about this.
Those extra holes in the Chevrolet flywheel I believe are for the dowel pins that are in the end of the Chevrolet crankshaft.
Best to stay with the GMC flywheel that is intended to be used with the GMC crankshaft.
