I have met a guy out in LA named Pete Grosso. He goes by Pete Echoplex on TGP and instagram. On Reverb, I think he's The Gas Station. He does complete tear downs and rebuilds. I have spent many hours on the phone with him in the last few days. Admittedly he was putting up with some Dr stuff on Thursday and I was on a 10 hour drive home. He ended up sending me a ton of photos of various models with pros and cons, specifically steering me clear of anything post 1973. Just a wealth of info.
Basically find your unit, get a picture of the motor and send to Pete. It'll run about 400-500 bucks for him to rebuild the entire thing and load up some NOS tape.
I texted him last night on something and he called me at midnight my time, 10pm his and we talked another hour. I'm buying the unit from a small shop in LA and he's picking it up for me and refurbing it. I will be happy to introduce you at some point.