I wouldn't worry about making plugs, some time on a bench grinder with some Home Depot alum bar you can get them to press in the intake, not the head. That being said, just realized that you shouldn't need low risers, you have a D2 head with an RPM right? Those are all med riser port centerline unless someone ground the floor past a med riser size.
A Mr Gasket 202A will likely seal better and is blocked already, If you really wanted to help it, then I would put something behind it, not plug the head side, harder to do and it could enter a valve pocket.