Im not convinced they need any mounting holes to be honest. After helping someone install some with only mounting/double sided tape they held just fine.

Agreed. In my experience, no screw mounting holes are needed at all. Just one hole at the back for the backbox hinge bolt to hold it in place at the rear and a couple of small pieces of double sided tape at the front of the sheet to hold it there.

The more important part will be the application of the felt strips on the sides of the playfield to stop scratching of the sheets when the playfield is raised and lowered.

swinks sounds like he has all this covered anyway.