Referring to the 1967 Chevelle Assembly Manual it says to staple each seal with 4 staples. There are 2 seals, 1 per side, so 8 staples in total. You would need some kind of h.d. stapler to be able to punch though, unless you are able to reuse the existing staple holes.
As for the seals themselves, there are 2 cuts or voids in each seal that run back into the seal, in essence creating three flaps. What the manual says to do is place the outer flaps over the rear body flange, while placing the middle flap under the body flange.
Timely question as I've purchased this seal for my 64 SD rag. Want to mock up the installation before paint so as to not disturb things after paint.
I now know to refer to my 64 Chevelle Assembly manual. Thanks.