I like! Your "jig" looks very effective.
You could probably take one of those vise grips and just dremel the end to a point, couldn't you?
I'm thinking about getting a small C-Clamp and dremeling down the "foot" - the end of the worm screw - into a point, then drill or ream a hole into the "C" side, the cast side, to allow a transfer punch to go through the body of the C-Clamp and use this as a "mini-jig", not unlike those "super jigs" for the AR-15s. You'd need two - one for the 4mm and one for the 4.5mm, aka 5/32" & 11/64".
You know where I'm going with this - I'd like to see a super jig for the AK, but it would have to be 2 parts, one parts only for the trunion like I just described, and the other part using the trunion holes as the index for the rest of the holes.