[demian5]

I just went through the exact same thing on a 60.

1st pic - Had a diff from a 80-90s cop car.
2nd pic - Got one from a 64 truck and had to add the wider saddles for the 60, and remove the track bar mount from the diff. Luckily the saddles were able to be welded on right next to the narrower ones (just like yours) and I used the existing ones to get the pinion angle correct.
3rd pic - Used the CPP deluxe track bar kit that put the pivot on passenger the trailing arm. Issue was that after installing that, no way I could put the shocks back in the factory locations. Had to extend the shock mounts as shown.

It all worked out but what a chore. Whomever put the car diff in used a conversion u-joint so all I had to do was use a factory u-joint and the driveshaft bolted right up. Before and after pics included too. Im running 1" spacers on the transport wheels on the truck to get them centered.

The diff you have in there should work. It looks like a 65 or later truck 12-bolt. The hard work is done. Just get a better shock arrangement. If you have the mounts at the rear of the frame, you could turn the lower mounts around and just bolt up some shocks.

Message me is you have any questions.