I was under the impression that the 4.0L spacers have to be used as they're thicker, I'm going to measure the crank and see if there's any difference. Reason for the downsize is purely financial, the guy loves the car, slipped a liner and 4.0l was 300$ , 88k so not that many milesYou'll need the spacers from the original motor to go to the original trans.
Torque converters were the same IIRC, so long as both were/are GEMS. It's been a while though, so double check.
Not sure why anyone woud go from 4.6 to 4.0......oh well, let's make a slow heavy rig even slower.