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I've checked the parts book and a value built catalog. The head gaskets and rocker arms are the same. Bore and stroke are different. The heads show different part numbers as do the valves and exhaust valve seat inserts. The MF parts book doesn't show casting numbers. In the value built catalog they show the same replacement rebuilt head for Z134 and Z145 with casting number Z134. The MF-135 parts book shows different exhaust Z134 valve seats depending on vintage, some alloy steel, some stellite. The material for the single style of exhaust valve seat for the Z145 doesn't indicate the material. My I&T shop manual gives dimensions for valve stems but not for valve heads. So its no help. My GUESS at the outside is that the heads come from the same casting, Just machined slightly differently for the Z145 engine, maybe a slightly larger valve head for the larger bore (3-3/8 vs 3-5/16) or always with stellite exhaust valve seats. Or maybe value built doesn't care but makes them all the same when rebuilt. Perhaps the real MF shop manual would show more detail. I picked up a supposed one on Cd-ROM from England but its most another model of tractor and engine and mostly useless. Be sure you get oil to the rocker arm assembly and that the corks in the ends of the rocker arm shaft hold the oil in so the rockers don't wear. They are a pain to fix. Gerald J.
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