What is it? A cool truck, that's what it is. But, as others have pointed out, getting the title transferred over may or may not be an issue. Buying parts will be fun until you know exactly what you have.
My '65 is like that, someone put in a 350 from a '70-ish Camaro, so when I buy engine parts I have to get them for that, but everything else '65 Chevy C20. I like your truck, even with the mix of GMC and Chevrolet parts on it.
