3800's have straight frame rails behind the cab. Installing 1/2 ton running gear will dramatically alter the angle of the frame rails and result in totally different handling and steering characteristics. I can't think of much of anything that would be a direct bolt-in swap. Even if you get the axles to fit, the bed won't, no matter how you alter the wheelbase. The world will just have another butchered-up, unfinished project rusting away in the weeds.
Jerry
