Well, I just happened to have the sport mirrors of my 69 coupe. I stuck a measuring tape on there, and measured it on the drivers side. I referenced the "leading edge" of the mirror control cable hole at 12in on the tape. The front hole is 3/4in in front of that, and the aft hole is 6+1/4in aft of that. A total distance between the holes of 7in.
If you don't have the mirror control cable hole, the best I could figure is the leading hole is 3+3/8in aft of the spot on the forward edge of the door that is "in-line" with the two mirror holes. The leading edge if the door is raked forward alot, so it was hard to measure accurately.
