'67 to '72 cab on '73-'87 frame questions

[stevek20]

Has anyone done this before? I have a 1975 K20, would like to shorten and put an earlier '67-'72 style body on it. I was wondering if anyone knows if the cab mounts will line up or at least be fairly easy to modify to work. Just to explain, I am confident enough to cut, weld, fabricate etc. if necessary but was curious just how close they were to lining up. I know, if its too much work I'd be better off getting the earlier frame and everything, its just that I already have a good donor '75 k-20. Any help would be much appreciated. Also- tried searching but does anyone know if the 1/2 ton frames are the same metal thickness as 3/4 ton frames, or are the 3/4 ton frames heavier steel? thanks