8-3/4 rear end question

[b5blueaar]

I have located a 1968 440 New Yorker with a 8-3/4 rear end (owner says).
Have not seen it yet.
If this car has a 489 case would this 489 differential fit into a cuda rear end? Or will the axle splines be different?

Also, the guy says the car sat for a long time then he got it running. When he first power braked the car, only one rear tire spun. He says now after a few burnouts, both rear tires spin. Must be posi.

Is this possible that it did not posi and now it does?
Does this indicate problems in the posi or just from sitting?
I may buy the engine ($300), but can get the whole car for $100 extra.  Would be worth the extra if it has a posi diff that can be used in my 71 or 74 cuda.
thanks,

[Chryco Psycho]

A 68 should have the 742 carrier but it will swap into your diff & the alxes splines are the same ,, posi sure grips can malfunction from sitting or wear, the 68 shoiuld have the clutch type sure grip & it can be rebuilt with new clutches  

[360 'CUDA]

No question

Buy the car!
So many parts so little time.