Not sure if any0ne has covered this or if it would even work but just food for thought. The Ford 351 Headers which can be sourced pretty cheap and came in Mustangs, Broncos etc fit the LS platform motors with the change of the flanges. In the Mustang world, LS swaps have become pretty common and a lot of guys will buy a set of longtube 351 Mustang headers used, cut the ford flanges off, round out the D port shape and weld on a set of LS flanges. Overall very simple and they fit perfect. I did a set and was into them for less than $200. That being said, I am not certain if they would contour the 3100 cab.