It seems to me that someone has tried to drill the holes originally and failed....., then sold the rifle on.

Can I make a suggestion? It's this. The sheer notion that you can screw a telescope front sight base to a No4 receiver ring and expect it to remain tight and soliud is the stuff of fairy tales. It ignores the basic schoolboy physics of rotational forces that you learned in your first year physics lessons at school. You know, clock and anti clockwise moments and all that stuff............... And whoever thought that small BA (or close to....) threads going into 3mm or so of mild steel revceiver ring would be sufficient to hold firm was living on another orbitory planet to the rest of the world. My suggestion is to ignore these holes, give the blocks you've just acquired away to someone you don't like as fishing weights and get a steel one piee easily mounted bracket to fit onto your rifle.

You were/are right. These blocks are an amateur DIY gunsmiths job