The fastest way to tell the difference between the 230's and 250's is to look inside one of the spark plug holes at the piston tops. 230's will have a flat top and 250's will have a dished piston. Those #'s on the distributor pad may or may not point you in the right direction, but in just a few minutes, the piston will give you a better clue.
Better yet, overhaul the engine, guess that it's a 250 and buy new pistons. Ignore that the pistons don't reach the deck, put it together anyways and see if it runs like crap and has awful compression. If it does, then you'll know it's a 230. Not as fast as looking at the top of the pistons, though. :-)
