904 front drum differences 71-72 solved, new problems

Apparently I got a 72-up rebuild kit for my 71 904. Now it's open and non-returnable. Looks like the lip seals for the rear drum/piston are correct and went in just fine. Inner lip seal was the failure point last time, and I'll confirm when I can air test. That brings me to the front drum/piston/seals. Obviously this was a change between 71 and 72. Question is can I interchange a 72-up 4 clutch drum with no problems? Or do I need anything else? I have access to a bunch of used parts and there should be 72-up drums there.

This unit had previously been rebuilt so I can't assure that all the parts are the ones that came in it from the factory. Casting dates would lead me to believe they are correct.

Yes, '72 saw a change to the narrow lip seals in the front drum and, yes, you can install a '72-later drum in your '71.

Perfect, thank you!

You can also buy the lip seals you need individually...

Maybe I'm missing something. Got a drum assembly from my friends part stash. Took it apart and shows its a 79. Physically identical to the 71 parts with the 70 casting date. What's the possibility it is a newer setup? Pics attached for clarification. 71 unit is on the left in the pics

Pic 2

Pic 3 with both drums

Is the groove for the lip seal the same? Can you compare the seals out of both drums and piston?

Every dimension I mic'ed was the same. Lip groove is in the same place. The original seals looked the same.

Transmission build date is Jan 11, 1971. Not sure if this could have been a possible mid year change. And again I cannot 100% confirm those parts are original to the transmission, just that was in it when I took it apart. I don't want to burn this thing up again, it's getting too close to race season now.

Guess it doesn't matter now, I upgraded to the later unit just in case.

So the next problem I am having is that I upgraded front pumps because the original reaction shaft bushing was loose. That ended up being part of the problem, it was the wrong year and had an extra hole. So I'm back to using the original if I can. New bushing fits in the reaction support ok, but it's not tight like I would expect it to be. What are my options besides finding a new pump?

Anyone? Loctite bearing sealant? Can I stake it in?