I'm putting one on my 70 as well, its in the body shop now. You can see the punch outs in the support frame under the sheet metal. I measured my buddies 69 428CJ factory scoop location at the rear middle of scoop to rear middle hood and it was 2 5/8" IIRC
One good way to make sure you have your holes properly lined up, is to: mount the screws into the scoop, and gently place it on the hood. Then,
use a few lengths of string, across the hood. Left to right, front to back. Where the strings meet under the studs, mark that exact spot with tape. Then drill.