He says that the rim diameter is increased enough that they no longer fit in a 45Colt/Cowboy shellholder, and he has to use the one he has for .455. I asked him what happens to the headstamp (... distorts a bit, but still quite legible ...) and also if there is a problem with primer pocket depth after swaging (... he says he noticed no difference.)
He paid a machinist to make this die for him, so I don't think he has any plans to put it into production. I'd have to confirm that with him, of course, but if he doesn't plan on it I could likely get the specs from him (and any suggested changes he might now have regarding the depth or diameter of the rim recess after working with this prototype) if someone else might want to start making them.
I found this whole excercise quite interesting, but I have hundreds of .455 Colt cases on hand (almost all Dominion Cartridge Company production) so I'm not really in the market myself. Quite some time ago I had fifty modified .45 Colt cases (rims thinned and shortened to .455 Mk I length) but once I had an adequate supply of .455 Colt cases I just wasn't using them, to avoid them getting mixed in with my .455 Colt cases since they required different shell holders, and eventually gave them to somebody. (Did the same with the cases from the only box of Fiocchi Mk II cartridges I ever had, since they took small primers and were sitting unused as well.)