Be careful with poly mounts just on the t-case and not anywhere else. They will not flex much at all compared to the stock motor mounts. So the motor is going to want to be twisting up and the t-cases are not going to let it so its going to put a good bit of strain on the tail housing and bell housing on the trans. I would at the very least put a tight chain on the motor.
If you go with the ruff stuff mounts make sure they will fit your block before you buy them. They will not fit a early model 4.0 block. One side is different from later model blocks so one wont fit. Thats why I had to make a set for mine.