to the majority of normal folks; if you put a factory aircleaner on there with "283" on it and some corvette finned aluminum valvecovers, they'd accept it.
I for one don't spend my time at carshows looking at casting numbers and other specifics. A smallblock is a smallblock to most people.
A purist numbers matching guy would know, or an engine builder, but if you're building a 60s era t bucket, does the displacement matter?
To the OP: you have several directions to go, just take stock in your abilities and evaluate the parts you have on hand carefully. You'll have a nice (307, 327 or 350 powered) truck you can be proud of.
There was a guy around here (HR.com) that had a 65 nova with glass fenders, hood & bumpers; little 14" cragars, M20 and a 307-based 310 out of a roundy round car. It has something like a 262H cam in it, manual brakes, manual steering and it was a HOOT to drive.