I would give Chris Weddel a call. They have been doing rebuilds for over 25 years.  I bought a five speed from them with a locking diff.  The locking diff acted up and they removed the diff and gave me credit with NO problems.  They shipped the tranny and UPS damaged it. I returned it and they upgraded my to a .457 ring and pinion from a .483 R&P at no additional charge.
They ended up giving me a brand new .457 tranny with 0 miles.

Robert