On both my PC guns the slide has a stamp matching the penned number on the barrel. So at some point there was on a bench at Springfield a barrel and slide marked #1. One has to wonder what gun that was.
I have thought about converting a gun to the Briley bushing. no going back from that though. I know Briley has a few of those threaded bushing in the bin back there gathering dust. That requires careful fixturing of the slide on a lathe and cutting threads. I've also tossed around the idea of somehow adapting an oversize 1911 bushing set.
Honestly I like my plain jane 4506 fine just the way it is with the standard barrel and don't plan to mess with it... too much
Cheers
Bill