I'm not sure if this helps, but..
Measured from the driver side, from the end of the rear crossmember, the first hole in the crossmember is at 4" and the second at 20"
Measured from the passenger side, from the end of the crossmember, the first hole in the crossmember is at 1 1/4" and the second, inner hole at 17" on center.
I measured with the tub and bolts in place.