A 230 has a 3.875" bore (3 7/8") and a 3.25" stroke
The 250 has the same bore and a longer stroke, 3.530". It should be possible to make a 230 into a 250 by swaqpping the crankshaft and pistons from a 250 into a 230 block. I believe the connecting rod length is the same on both engines, but the compression height will be lower on the 250 to make up for the longer stroke. A 307 V-8 piston will fit the 250, same diameter, weight, wrist pin size and compression height, but it's a flattop design where the 250 has a 1/4" dished top.
Either block should take a maximum overbore of .060", but .030" oversize will give a longer-lasting rebuild due to thicker cylinder walls. 60 over engines have a habit of overheating easily.
Jerry
