[Rickybill]

He did drill in from both sides.
Because the hole is not centered on a flat surface, some tool - I'm not a machinist - was used to cut down to a point where the drill could go straight in without wandering.
The pin was fixed with green Loctite.

My gunsmith will drill the hole and install a pin for $50, if anyone wants that part of the work done, leaving the fitting to the owner.
After his experience with my breechblock, he can do it again much more easily than the first one.
This is a terrible picture, and that's why I didn't use it before, but you should be able to see the pin, with the part blocking the bore of the breechblock reduced with a small, round needle file.