My advice would be to call James Northum in Texas. 4 hour drive from Norman. But well worth it. Jim Fulmer used to drive down from OKC for all his transmission needs.
I can vouch this isn’t for the RC all over FakeBook that runs 37” mil tyer’s that does downhill burnout’s towing a trailer at 70mph! There isn’t a THD sticker on this rig and it actually runs.... This is my fondlers built unit and got a bum deal on a “working” transmission..
There is a fella in Sparks that just rebuilt my neighbors 68rfe that he is very happy with, and the price was very reasonable. I’ll have to post back after I find where I wrote his name down.