I would not use rubber, it will pinch out, or crack, or bleed out.....When I was body working the car for paint, I had to use a body hammer and gently pound the areas around the bolt holes to straighten the hood. The gaskets that Classic sells are made from plastic which will gently conform to the hood and scoops over a period of time. If I had to have them..... this is the route I would go, although A body cars did not have these installed, not to my knowledge.
