When measuring for frame re-alignment, make sure to measure from points that are usable on both the old rails and the replacements. Again, MCR has a jig, but if you are doing this at home, a string and plumb bob can be used to mark for re-alignment. If using a plumb bob, hang the string from a location on the old rails that is perfectly repeatable when the new ones are in place. Simply hang the plumb bob, and then mark the location on the floor. Always remember to measure several times before cutting.