If they are Skylark and have the factory moulding holes already drilled?..I believe one of the pre-drilled holes is already in the correct spot for ventiports. I had to replace one of my fenders and it was easier than I expected. You can line up the stud on the ventiport and mark your pattern. After that I took a cut off wheel and made an X pattern in each of the rectangles connecting the corners. Just have to be careful and trim holes slowly with a half worn out wheel so it fits into the rectangle. Those fenders are a steal if you need them?.I have never seen a nos set before.