[70LonghornCST]

This is a good question. My question is are you using 67-68 or 71-72 bumper brackets? The bumper brackets are definitely different. I am not sure on the overall geometry of the bumpers when comparing a 67-70 to a 71-72 bumper, other than the turn signals being embedded into the the bumper on the 71-72, and the GMC being specific in itself 67-72. I believe if you use the 67-70 brackets, a '71 bumper should fit on a '68. I'd wait for some others to chime in who may have actually done this.