In another topic I discussed how I'm also considering this kind of project. I was thinking, since the vehicle would be converted to 4WD, I may consider a 2" body lift kit, to increase clearance at the rear edges of the front fenderwells, but also to increase space for the engine and transmission to clear the doghouse and the firewall opening above the engine. I have not seen a Cummins powered van in person, I wonder how tall the Cummins is, compared to a PSD?
I used to drive a Ford van with the older 6. 9 liter engine, and the noise to me was tolerable, as HoleshotHolset mentioned.
Andy