My recommendation would be....DONT. In order to do an interchangeable system, you will have to install a drum into the barrel. In a 45 cal. barrel, 13/16" straight, you only have about .170 barrel wall......this is not enough to safely do it.
Besides, in an interchangeable system, you will be removing and changeing parts....they will eventually become worn and
unsafe. I would recommend you build it as a flintlock, save some money by not buying that percussion lock, and buy a
Chambers small siler flint lock, this would be the best way to go...........Don