I haven't done this, but I believe that the 73 and up Blazers are about 6" longer , just like a shorty pick-up. I don't know why one would switch to a newr frame the OEM frames are a good design and have better bracing at the steering box. The best way to do it (I'm a welder) would be to set up an "A" frame over the project, rig the body onto the new frame, line it all up, then remove the cab mounts from the frame and mount them to line up with body (you might have to modify the mounts or fab new ones) making new mounts for the body would be alot harder than changing the ones on the frame. Make a "Zero line" to take all measurements from or you'll never get it right. The wheel-base is longer on the newer frames so you'll probably need a bodylift ( the frame heights will be different) as well as a suspension lift if not some fender triming. You could also line the body up with the front suspension and then move the rear axle to suit, way better idea than trying to move the front axle, what with all the steering and such. Any way you do it it's alot of work to do it right.