My main concerns with the complete drivetrain swap is bay length, gearshift location, and steering. The engine bay should be long enough judging by my eyeball but i understand a radiator may need to be moved forward some; plenty of room for that. what do you think about gearshift location? Steering, I have a feeling, is going to be a mess of adaptations.

You suggested a 7.3 IDI and I agree it makes sense. there is just something to be said about having something in your truck that no one has heard of. I bet 75% of the ford guys have never heard of the 6.9 IDI and probably couldn't tell the difference between the powerstroke 7.3 and a IDI 7.3.