Here's one with the V-ASA just drilled and tapped for a 10/32 screw.
Line it up on your rail first. Your best bet is if the ASA sits snug against the trigger frame with the 1/4" NPT hole still well in front of the mounting hole in the rail. This one worked well on a tac-1 rail, but not so well on the am/mm rails. That's why you can see the spacer in the pic. I needed to fill that gap to make it sit tight.
Mine is drilled all the way through, but back far enough so that the airway isn't compromised. And then it's tapped all the way through for 10/32. If it is not sitting snug against the trigger frame it has a little wiggle, but very little.
and so you can better see the relation of the holes: