An Amiga 1200 in a tower is normally referred to A1200T because it is in a TOWER!!!!! The T standing for TOWER!
ie: POWER TOWER.
By default, the Amiga 4000 is a way more powerful system than the A1200T. Having said that it is possible to put A4000 cards on an A1200 using a busboard:
But like someone said, it may interfere with other cards. I don't know.