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I have parts of a 220 from a 1959 military tractor. (Pistons did not survive.) On the crank, the rod journals are larger, and the mains are larger than the front and center in a regular MM engine, and all the mains are the same size. Years ago I rebuilt a 220 out of a U302lp and put it in a jetstar3super. The compression distance in the pistons in that 220 engine was about 1/4" shorter than a standard Z piston. I happened to compare the z piston to one of my old 220 pistons later. I DO NOT think the blocks are taller. That would involve a longer oil tube, longer push rods, and a different water pump mount/front water entry tube and upper water return for the engine, but I DO think the connecting rods in a 220 might be a corresponding 1/4" longer to make up for the shorter compression distance in the pistons. The 220 I rebuilt fit right in the jetstar with no modifications. (I even used the U302 flywheel and clutch.) I used all the jetstar water tubes from the old engine and everything fit fine. I have wondered if when designing the 220 whether MM used an existing piston from a GMC 305 V-6 engine, but I can't confirm it.
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