Fibonachu...the center of the crossmember. Per the instructions from Speedway, you had two options. One was measuring from the center of the front spring perch bolt hole and the other was so many inches back from the front of the frame rails. That is how I'm now finding I'm off by the quarter of inch. (measuring each distance to the center of the crossmember). I suspect that when I used the template on each side I had it correct, however the frame is that much out of square.
