[big job]

Sorry I think you have to pull the heads and measure the bore. I know cause I have two 1956's that have yellow blocks = a 272 But color after all these yrs don't mean too much.

Could be the first 239? could be a 272, could be a 292, could be a 312?? You may want to pop a valve cover off, does it have lock nuts on the rocker arms = that's early, if not that's later, maybe 1957 and up till the end. all I can say. sam