I'd just clamp em in a vise, drill them out with a good hand drill (or drill press if you have access to one) as vertical as possible and hand tap 'em.........The taper and thread tape on your AN/NPT fitting is what seals it, so it dont need to be anywhere near to close to CNC accurate......But I'm a cheap bastard.........

If you dont have the proper 1/2" NPT tap or drill, well, then $26 becomes pretty cheap really........
Ray