Mercruiser has a habit of putting some pretty radical grind cams in their marine engines, but without doing a check with a degree wheel and a dial indicator it would be hard to say what might be there. You might also find a set of forged pistons in the Mercruiser. The bore size on the engines will be the same- - - -the difference in displacement comes from a longer stroke crankshaft, and pistons with a different compression height in the 250. Check both engines for taper wear in the bore, and use whichever block has the best condition cylinders. If you really want a 250, the crank and pistons from the 230 won't work. The block, heads, and connecting rods should swap OK.
Jerry
