need help shortining 76 quad cab wb

[painlessjake]

I have some ideas on how i should go about this and will surely overkill it but this truck needs to b strong. I started with a 76 quad cab dually from "stonecarver" and its getting a built big block,th400, divorced np205, 14 bolt and looking for a 60 but my conundrum at the moment is im putting a step side short box on this truck and need to shorten my wheelbase. I feel cutting the frame is the best way to go about this im just looking for feed back as to where to make the cut???????? please help