I've shot BP rifles and smooth bores for many years, so I know all about not leaving a air gap as it cost me once many years ago, but we won't talk about that....

During my research, I've decided to us Wonder Wads as a filler, mainly so they don't crush the powder during the bullet seating. I have found over the years that no matter how close to doing it the same everytime, when you get to crushing BP your loads change. I've also looked at loading with American Pioneer Powder which is also a substitute.
As far as the rechambering, I'd likely take it to a pro as I've never dug that deep into guns and wouldn't want to ruin one trying to do something I've never done.
You are right about Quigley, he was shooting a 45-110 with a 540gr Paper Patched bullet, or so the movie goes....

BTW thanks for the advice!!!