kohler engine conversion

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I need someone to tell me if there is a conversion table were you can fine an engine of any brand to fit a tractor. My Massey Ferguson Legacy has a ch25-68583 kohler engine in it. It was change to a ch730-0014 which they don't make either anymore. Somewhere I got a chart in kohler web site that I could use a ch740-3115 but it can't work because it has and 1 and 1/2 inch shaft and mine is 1 and 1/8. An engine dealer told me that an ch740-3165 would work. It does have the right size and length shaft but the air canister won't be able to fit under the hood and when looking it up that one is for a grasshopper. Does anybody were I can look to find the right size replacement motor even if its not a kohler. I like to find a rebuilt one or used at a good price. I will travel to pick it up if need be. My motor is shot and need another one