[jeffspower]

A 545 Allison off maybe an IH or Cummins motor should bolt right up to the SAE pattern. You'd probably have to engineer a way to bolt the TQ to your flywheel & maybe a bushing to center the snout in the crank. A friend has a IH S- series that originally had a 7.3 & 545. He blew the engine, and put in a DT466 out of a twin screw. It bolted right up to the tranny. Shift points are not quite right, but it works. Someone needs to do some valve body/ governor calibrating for him.

If you want a 13 speed, his is probably just sitting there. I think it's an LL model. About 250 rpm between shifts (IIRC), but no OD. First gear would be about .3 mph @ 1000 rpm.