Thanks for the info. I looked at the chassis today. It looks like the rear cab mounting holes on this 1/2 ton are diagonal like the chev. The only real difference I saw so far is the radiator is different. I suspect the core sits about 3/4-1 inch farther forward on the GMC due to maybe the engine is longer than the chev. I think the mounting holes may be the same. I plan on comparing dim. on mine tomorrow to verify as much as possible. So far so good. Thanks again.

Roy