What are the dimensions of your crankshaft snout? Chevy 6 cylinder engines and small block V8's have a 1 1/4" diameter crank nose. The OD of the balancer snout is 1 3/4", which will be the same size as the lip of the front seal. I'm not sure if those dimensions will be the same on the GMC engine. If they are, it might be possible to modify a Chevy balancer to fit.
Jerry

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