two wheel and 4-wheel frames are different up front.
There is a difference in the 'kick-up' for the front suspension.
Also--the rear suspension is the same as far as springs go (4x4 and heavy duty 2x4), but the rear spring hangers are big time different.
Full frame change would be the easiest route in my opinion.
At least going to a 2-wheel drive from a 4x4 there would be no
floor cutting in the cab.------4x4 cab floors are different than 2-wheel drive cabs