I believe GMC had leaf rear and Chevy had coil, you have leaf. So gotta think on this. If the rivets are legit, maybe a GMC chassis and cab structure with original info Plates. Loaded with Chevy body parts?
Both plates are in the correct place on body for 1965 GMC. The kick panel plate says the correct 305 V6 that it came with. All info says the rivets are NOT correct for 1965, but it is possible that the factory used other rivets if supplier problems and unknown reasons. The front frame/motor mounts were a little different between Chevy and GMC I think. Maybe there are remnants of a BB 305 V6 being in there? Guessing GMC frame with the plates from that GMC and has a Chevy body. Not a true Chevy or GMC.

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