That's a 1955 or earlier frame, not a 1957 frame.
And the engine looks like a big-head Bullet (Fury) engine.
Don't know how far back the Fury goes, but with that engine, that's my guess.
As far as I know, there were never any numbers stamped on the engine which directly designated year of manufacture, so if there's a 57 there, it's probably just part of the engine number.
The number on the front of the crankcase (well, on the twins, anyway) is supposed o be the same as the gearbox number.