I understand the want for a diesel, however if the 351 was in good shape I think I would have kept it over the 6.9. I had an 89 f250 with the 351, it would pull anything and when we pulled our TT we passed a lot of smokers (6.9) as they struggled up the hills. Forget the HP of 6.9 but it was only around 200 as I recall, the 351 was about 275-300 or something. I also had a 10 ft slide in camper in the back and it would haul it and aghain we passed a lot of smokers, but the mileage was nothing to write home about!
Anyhow as long as you understand that there is little support for the 6.9 as far as aftermarket you should be ok. The only turbo kits I think were Banks and you might want to look for one, but check with banks 1st to see if it would work in a van enviro.
For the best of the camper you can raise the 'trailer' you made, get a 4K generator, add a house ac (5-9K btu) some electric and then you will have it all good to go. Check for some used rv stuff on CL like small 3 way refrig's etc, dont waste time with sinks etc. Easier to have something out side with water supply (trailer?). Porta potty up to you. My brother had an a chebby van with the camper mod, had all the inside stuff not a lot of room. Had to make the table into the bed when needed (he was single so never had a table