Stay with the complete OMC rotating assembly. They're in the business of making their engines stay together, so don't second-guess their choice of parts. I did a similar buildup on a low-hour 454 with 4-bolt main bearings from a houseboat. The dummy owner let both engines freeze up. One pushed the "freeze" plugs out, but the other one cracked the whole side out of the block. I got a new, semi-finished block and bored/honed the cylinders to fit the standard bore pistons. Parts & labor plus dynamometer time cost him about $4,000.00 before I was done. That was an expensive stupid attack! I'll bet he doesn't procrastinate about winterizing the boat again!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!