If both axles are pulling out of the diff I'd say you probably found the real problem. If you were the stepson and were doing neutral drop burnouts in Dad's Mercedes and blew up the rear end, what would your story be?

"Gee, I dunno, Dad, I just got in and started 'er up and she it wouldn't move?!?"

I think if the price is as good as you say I'd jump on that deal. Tow it home, make a trip to the boneyard and get the right diff and put the right one time the first time and be done with it.

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1984 300 Coupe TurboDiesel
Silver blue paint over navy blue interior
2nd owner & 2nd engine in an otherwise
99% original unmolested car
~210k miles on the clock

1986 Ford F250 4x4 Supercab
Charcoal & blue two tone paint over burgundy interior
Banks turbo, DRW, ZF-5 & SMF conversion
152k on the clock - actual mileage unknown