Roland;
I think you are going to run into problems when you try to replace the drums, with touch hole liners. The drums on CVA guns have large threaded sections, with metric threads, on anything but the very old CVA guns. This would give you few options other than cutting off the breech, and rethreading, both the breech, and the touch hole. You will rapidly get more work, and money tangled up in this project than its worth.
As for the O/R barrel project, I did one with an old lathe a local farmer let me use in his barn, and a couple of good big files. The lathe is only needed to knock the corners off the front part of the barrel. The contouring is all done with a couple of files, held against the now round section, to give it a little swamp. Finish up by using the big flat file as a backer for some good sand paper.
Hungry Horse