I'm dropping a 12 valve into my 03 and it will fit not bodydropped for sure, but not sure how much extra room. Not sure how the 03 engine compartment compares to yours.
I was curious about the same thing, I'm going to be doing a Cummins swap in a 76 this winter. Haven't seen anyone body drop one with the swap. I didn't want to jack your thread though since it's a different bodystyle.
ive got a box style dually and theres no way i could ever stuff a cummins in it with it bodied....my truck is Z'd 2 inches and stock floored 4 inches...my LS motor wont even clear hood and it not near as big as a Cummins