I think you're exactly right. I looked at some pictures of Smith V480's and it does look the same! The guy said that it was a Quincy compressor mounted on a Smith tank; not sure where he got that idea except both companies were located in Quincy at one time.
The old guy said that he looked again and it is marked Smith on the compressor.
He didn't write down the model number though. I decided to pass because of parts availability. Seems to be the V480. Single stage, 4 cyl, 5hp, @ 16cfm/150 psi.