Grouse,
I have a couple designs that I know will work, one I am currently using. If you want to make a good plug that works 100%, you need to go in the other direction that Knight chose.
Is he looking to incorporate the FPJ, or the NFPJ bolt adapter? 209 primer, or LRMP? I have designs ideas for both, but nothing on paper.
If you ask me, the LRMP is the way to go. If he is interested, let me know. I could probably whip up a couple rough prints for him to ponder, if need be.
You might not want ideas posted on the open forum? There may be others looking to do the same thing now that Knight won't be working on it. There will be a market for this plug, big time.