I just measured a CJ2-A frame for you. There’s no reason to believe that it’s any different. From the rear crossmember (not the ag hitch mounting brackets, but between them, on the frame), right down the middle to the middle and center of the round crossmember, 109-1/4”. Hope this helps. BW
My 51' CJ is missing the front crossmember, the front of the frame was replaced some time ago and front crossmember was removed. The front bumper is welded to the frame I guess to make up for this. I am going to replace the crossmember to it's original location. The rear cross members are still there. Does anyone have measurements from the rear frame crossmember to the front?