Ok, I just snapped these pics for you of my trucks frame, where the front hanger bracket is mounted, and just in front of that. Keep in mind that my truck is a short wheel base, but an extended cab. So, the bed will be the same as an gmt400 short bed (6.5 feet) but the frame is longer under the cab. Still, this should give you some reference as to where, and how you need to shorten the frame. You will want to do this where the frame has no bends. This may mean, you will need to remove the cab also, IDK. If you need more pics, just let me know.