Kinda done this the wrong way but have epoxy'd a nut to the mag well so it can be held in place. It is just a working prototype (or Tinkertype lol):
Also, you will see I cut an additional slot (right by the epoxy'd nut) to make clearance room for the nut/bolt that holds the front of the grip/mag well to the body. I am still currently meeting my goal of having everything unboltable for maintenance. I'm not pretending it isn't a bit fiddly at present, I will have to epoxy or otherwise make captive some of the other nuts to make it easier for assembly.
EDIT: Also picked up some 1" square tube just to experiment with regulator placement, and gonna try out some black plastic-dip spray for the first time on the metal parts to see how that works out. If it sucks I'll just use satin black or something.