My vote is to put a CTD into an existing Crew Cab. My truck started out as a W350 360 727 NP208. I located a totaled '92 W250 (drive train only) CTD inter cooler, Getrag, NP205. The engine was complete right down to the alt. & AC comp. Forget the exact cost of the drive train, but it was around $3000.
The items that had to be modified in my case were:
1. Transmission cross member. Moved up 1. 5"
2. Radiator support from a '92 salvage ($15)
3. Radiator ($300)
4. Added an extra leaf on ea. side due to the increased weight ($200)
5. Exhaust system ($250)
I have access to an engine lathe & mill & made the necessary parts to keep the original grill. Some cutting was required on the radiator support in order to make the head lights fit, it appears the later models head lights are higher up & further apart.
The actual conversion took me & two buddies two weekends.
Completed the conversion about 2. 5 years ago & have not noticed any frame twisting or damage but I have only towed heavy a few times. I do wish I would have boxed the frame, if anything for piece of mind. Overall very happy with it.
Doug