So i'm wondering if ya'll could help me out...
My '79 245 needs a new manual trani, grinds going into reverse (this has been going on for 2 years now), O/D stopped working suddenly 2 weeks ago after the car had trouble engaging 2nd, 3rd, & 4th and produced very load shuttering noises. For the last year and a half it's also had occasional trouble engaging 2nd, but never any O/D troubles, asside from the broken wire or low trani fluid, (it also leaks like a sieve, so seals have been needed for a long time too).

So i found a good transmission shop here near work and asked their opinion. The owner said a rebuild would be $800+ and is the car really worth that, since it's got roughly 210K miles. he suggested that if i could find a used trani they could install it for $150 or so and if anything might need to be done to it, i would still be coming out ahead.

I found a 2 used M46 w O/D at a junkyard in NH, one '76 & the other a '78. I drove up there and picked the '76 up for $150, the '78 was missing some parts and the older one was more or less complete. Not thinking there was any differences I decided on that one.

I dropped the car and trani off at the shop. They dropped the trani and immediately noticed that the '79 has a fine spline drive and the '76 has a course spline and several other significant differences, not at all interchangeable as we thought. So now what do I do?!

These guys were gunna call up to NH and find out about the other trani. Anyone know if '78's are interchangeable? If they're not, it appears as though these are perrty scarce, the next place I found one was at Revolvstore in AZ and they want $650 + $200 shipping.

I think I'm almost to the point of just biting the bullet and having the trani shop rebuild the thing. So i'm asking what anyone out there might do or has done, or if they know of a decent used trani for my '79 at a good price.