I would call a few other shops. When I had my SM420 rebuilt two years ago, one shop told me $800-1200, the other shop told me $400 and up depending what it needs. I went with the lower bid shop. Once He opened it up he said it only needed synchro's and gaskets. $450 was my total after tax.
If everything seems to "work okay" why not install it and give it a try? I can remove my tranny out of my '48 in 15-30 minutes depending on my motivation.
Curt
