[larrys40]

Bill
I would do a couple preliminary checks to help pinpoint what’s going on.
Pull the floorboard and pull the 6 bolts that hold the transmission shift tower into the top of the trans. Make sure there isn’t a shift fork issue and the trans isn’t in two gears at one time. Be aware, never , I mean never start the car with the trans top off as you will coat the headliner and interior with lube.

If all that looks good I would then next see if either rear wheel will rotate with it off the ground. Try both sides. If one turns and not the other pull the rear hub on the stuck side.
If all is well then I would just plan on pulling the rear axle back to check the u joint and then driveshaft condition. You will find quickly if you have a u joint and or rear axle issue.

If there is someone in a local model a group that is rear axle savoy it might be good to recruit them. I’ve done lots of rear axles but I’m in the Midwest. Brent terry is eastern Tennessee and he’s aprofessuonal shop if you don’t feel inclined to tackle it. If you have les Andrews shop manuals they would be advantageous if you wish to tackle it.

U- joints, gears, bearings fail so it is a matter of methodical elimination to pinpoint.
Hope that helped.
Larry Shepard