post some pics of the inside of the tranny, you may find that filling it with some diesel and letting it sit for a few days, it may clean up enough to run a bit. Rusty gears can be cleaned to be made serviceable a lot of times, bearings, probably not. The case is probably the least hurt by rust, but hard to tell without pics. I have no idea on one that age how hard it is to find another trans to drop in.
