I think he is asking is it easy to swap out a 6.9 to a 7.3. To that question, I have no idea. I would imagine it isn't very difficult. It's already a 4x4 4 speed. Exhaust and driveshaft would be the biggest problem. But, is the bellhousing pattern the same? I don't know
The motor swaps out easy, just remove and replace. The problem is the wiring, You have to change a bunch of stuff to switch it over to the 7.3 style for the glow plug system. If you stay with the 6.9 style It can get expensive to replace that module on the back if I remember right. I also think the 7.3 style is a little less trouble free.