Tom,
No Problem, I thought maybe my BFR submission didnt go through. Glad you asked on the Stinger as its pretty cool how I did the DD.
I basically did the same thing in my upscale MR-1 the MR64 and close to it in my GIZMO XL. The Av-bay is in the NC coupler, Shear pins hold the coupler into the NC & BT. I was concerned with one, the drogue charge jamming the coupler in the NC and two, the thrust breaking the shear pins and having the coupler slide down into the BT, I'm flying a 98mm CTI K4000VM at Red Glare so yes this could happen. Both issues I solved by using a 1" band of coupler in the NC and a 1" band in the BT.
I use a quick disconnect so I don't need a switch band on the coupler itself. Vent holes are positioned as far down the BT as possible, my Av-bay also uses push button switches so it can be turned on right through the vent hole or a separate smaller hole. No the positioning of the holes won't cause your altimeter to be spoofed, I've done a many times with no trouble. For barometric units I use a 4 second delay just to be sure.
For the NC coupler I used your standard Av-Bay bulk plates, because I'm using my 4" Av-Bay I cut the holes in the bulk plates to match it in size. I used the all threads only cause it was easier when putting it together.
As I said I use quick disconnects on my Av-Bays so alls I have to do is insert the bay in one end, connect the quick disconnect and screw on the wing nuts.
For the NC shock cord attachment I took a 3" bulk plate and a 6" Eye bolt. I drilled 4 1/4" holes in the bulk plate, you unscrew the aluminum NC tip, put the 3" bulk plate on the eye bolt and slide it into the NC, screw the NC tip back on and wrap tape around the joint to seal it, now pour some epoxy into the tip, this with secure everything and also keep the NC tip centered.
As I said Shear pins will hold the coupler into the NC & BT. I was concerned with one, the drogue charge jamming the coupler in the NC and two, the thrust breaking the shear pins and having the coupler slide down into the BT, I'm flying a 98mm CTI K4000VM at Red Glare so yes this could happen. Both issues I solved by used a 3/8" piece of coupler in the NC and a 1" piece in the BT. You can see the band in NC in the above pic and in the BT below.