Forget the 3600. Re. your 48, not sure if you said the stock trans worked or not. If the stock stuff works, shifts good etc. you're fine. If you have a junk 48 trans and cannot rebuild it and or the vacuum shift if bad, then you need to think about this later type trans. Now lets say you need to swap to a later type trans or change the stock unit to later type H box, call Buffalo re. shift levers etc. he is the GURU on all this stuff and can really solve your problems. Buffalo has the BIG ad on home page of this site.
