If indeed the chassis is a 57, there were only two V-8's available then, a 265 cubic inch, and a 283. Assuming it's got the original engine still in place, look for a machined pad just ahead of the passenger's side cylinder head and copy the letters at the end of the stamped number. Someone here should be able to decipher the engine size and application from that suffix. There are several online lists of engine ID codes.

Welcome to the nuthouse!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!