If he's giving you horsepower at the wheels, thats not a horrible number. Probobly represents around 365 - 375 crank horsepower. If its a low compression 440, with stock heads and a few bolt ons, I'd say thats a real world number.

Just because we say that its easy to get 500 hp out of a 440, doesn't mean that every one on the street is making that. Sounds to me like all this motor has on a bone stock 375-horse motor from 1970, is a little cam (that may not match up well with the intake and compression), and a good set of headers. If the last valve job was done by a yeah-hoo, and it was built, compression-wise, to live on 80's pump gas, then I think it all makes sense.