Thanks for the additional insight.
I'm aware of Bob Snapp's rimless extractors but haven't encountered one to date. Is he still alive, and are they still "out there"? .221 Fireball is another one kicking around in my head.
.20 KCF: new one on me. Details?
Another thing to caution the OP regards the firing pin. A conversion to a higher pressure cartridge, wildcat or not, entails bushing the firing pin hole and installing a smaller diameter pin. Perhaps not a tremendous concern unless pressures above pistol cartridge levels are in the offing but why skirt the issue if doing the job right?
One of my current Cadets may have just moved up the list of "round tuit" projects. Thanks, ya bunch of enablers!
I might also recommend Treebone Carving for new wood as the project unfolds. Great folks to deal with, nice pattern options for Martini cadets.
Regretfully, Bob has passed on. https://www.stephenson-wyman.com/obituaries/Robert-Snapp-2/#!/Obituary . He was one of the nicest people I have ever talked to although I never had the pleasure of meeting him face to face. He was quite different from a snottty West Virginian well known for his handgun sights that has to be the rudest p*r*i*c*k I have ever met.
