For a gun that has been shaved, I recommend using .45 AR brass. You may have to trim the cases to length* and you will have to thin the rims. That is done on a lathe by just cutting the rim down from the front. It can also be done on a drill press with a half-inch chuck by using a safe-side file. The .45 Colt can be made into .455 the same way, just more case trim is needed.
The same technique can be used to make Japanese 9mm revolver ammo from .38 S&W. After the case rims are thinned, size in a 9mm or .38 Special die.
*I say may, because the chamber leade of those British revolvers varies a bit; usually, the .45 AR will work fine as far as length goes.