Where are you in California? I have a few places I can send you to. Magnums have good ring seal well in to the 120,000 mile range. Anything before that I wouldn’t worry about. Usually a set of bearings gets you on your way. Bonus if you can hear it run and see the oil pressure before buying.
https://www.hughesengines.com/Index...bnVt&level1=VmFsdmUgU3ByaW5ncw==&partid=35162
Use the stock Magnum flexplate with the 904. You’ll have to elongate (Waller out) one hole to make the bolt pattern work.