What size carb?

That equation is a decent deal to find a baseline.

But why does my 360 that only needs a 750, according to the equation, run much better with a 950 or 1050 on it??? Hmmmmm!

A 600 carb is a decent choice for the OP's current engine, IMHO. On a manual trans car you can get away with more carb. I run nothing short of Holley 750's on 340's, manual or auto cars.