Here are some dimensions, verified off two of my '68's. Dimensions were within a couple mm of each other. the front is to the rear edge of the fender not the other holes as it was of the car on one and only pre-fit before paint and not fully adjusted on the second.
HTH
This is the rear part under the door. The circle is the rear wheel area, the two black lines where the seam is between the rear 1/4 and rocker (ends up being pretty much top of molding) and the rear wheel arch.
<<<========Front of car The distance between the hole pairs is consistent all the way forward, 3 more pairs under the door.
Front fender, just a measurement from the edge of the seam between door and fender forward to the hole, same horizontal reference.
<<<========Front of car
I use the Picasso School of Sketching!