I did the same, and got my 42RH out of a 2 wheel drive Dakota that was front end crashed.
Dropped the pan and it was super clean with bright red fluid.
One thing I see (or don’t see actually)
is no one ever mentioned needing to swap the cooler lines out for 3/8 since all the old TF 3 speeds had 5/16 lines.
I used 3/8 tubing with a non scuff coating called “Gator something”.
It is actually Semi truck air brake tubing.
Then NPT to 3/8 compression unions in the case and cooler.