on my 71 truck i used an 85 swb frame----i put an 85 stepside bed on it--(in the factory mounting holes)---the cab of the truck only located the front cab mounts on the correct position on the new frame--the rear cab and radiator support had to be made to fit---you will also have to notch into the dash to point your steering column at the new steering gear location---it may be possible to put 2 joints on the steering column---the cool thing is you can reuse the modern diesel frame tank and ditch the behind the seat tank----that will make your oversize relatives happy....ohoh---just went to check on the cab mounts---maybe wrong---i did this job maybe 10 years ago---it looks like the rear mounts on cab line up with the rear cab mounts of the new frame---but the width is different--i cut off the original frame cab mounts and put them on the newer frame....