Ok I have a 93 MM. the engine is getting tired (264k) and i just picked up a 91, 6 bolt engine to rebuild and put in the 93. other than the obvious 6/7 bolt cranks, what other diffs are there? I do see different part # for the main and rod bearings, and oil pump. how different are they, size/ width? which is better? Thanks for putting up with my ignorance.