My take on this would be that an additional barrel fitted sometime later would certainly be OK depending on who fitted it of course. Not that it makes any practical difference - just sorta the "feel" of things. Nice to know that the big pieces were meant to be together kinda thing. Having said that, my fave pigeon gun has a non-original factory fitted barrel, and I recently scored a primo like new barrel that I fitted to an older Mirage that I like a bunch. And the new barrel just fits and shoots killer.
And even tho Perazzis may not have any real collector value the number of butchered ones is boggling considering the market value, and unbutchered ones get a better price. I would wonder why an SC3 would have needed a new barrel?
but that's just me
Dr. WtS