You’ll recoil in horror when I tell you this… One of my first forays into this hobby I managed to get my hands on a Pat vintage folmer and bodged the hole alignment for the grip rivets, the drill bit skipped around and they were up and down all over the place. I did this with a hand drill without a guide dent… thing… tool, to pop a dent where the drill goes. I’ve since learnt my lesson. If you are able to get hold of a pillar drill (my friend has one) that’s ideal. Though honestly I don’t drill the holes under the grips anymore. I just pop the rivet, cut them short and glue them to the grips.