There are six snaps on the top of the frame. The frame itself should measure 44 13/16" in total length. One hole is located in the dead center of the length. Looking at the frame from inside the car (LHD) and moving to the left from the center snap; three holes are located 9", 11" and 20 31/32" from center. From the right of the center snap, two holes are located 10" and 20 31/32" from center.
If you have a top on your car already, you might want to check and be certain that this spacing works. Incidentally, I recommend using the original type expandable snaps versus the thread in type. You would be well advised to make the new holes in the frame with a milling machine. Don't try to drill them out or you may bugger up your frame. Good luck!