Another problem that might come up using the GMT 400 ('88-'98) chassis is the width of the frame itself, I do beleive that they are wider than the old 34" std frame older trucks use. I do know that it made aftermarket utility and dump beds a very difficult fit when they first came out, GM had to release a 2nd version of the 3500 with a 34" rear section so as not to lose the tow/utility/light dump truck industry. This might cause issues with the cab mountings bed mounting,and the running boards. Another not on the GMT 400, the frame is wider in the middle, and tapers to the rear, this will cause issues with shortening the frame.

Bill Burmeister