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.

Please refer to the scanned page attached:

 

On my 64 Beaumont and 64 Chevelle I used copper for the staples as they won't rust.

I took the ground wire from household wiring 10 or 12 ga 2 wire and bent them up as big or small

as I needed and just drilled holes for size.