Rear bumper swap 74' to a 73'???

It may or may not. Could depend on if you have the shock type bumper mounts or the more standerd kind.

But if it does not just bolt up then all you should have to do in bolt the mounts to the bumper then hold/brace it up there where it goes on the back of the car then mark the bolt location on the back of the car using the bumper mounts as a guide. Drill them out and mount the bumper up using bolts with nuts on the back.