To convert a .455 to .45 ACP, the cylinder is set up in a lathe, and faced off, to increase the gap between the cylinder and the breechface. This makes room for the half moon clip, or the .45 Auto Rim cartridge's rim. From the photo of the left side of your revolver, it would seem unlikely that this was done. When a .455 cartridge is placed in a chamber, how much space is there between the cartridge case head and the breech face? If there is a substantial gap, the revolver has been converted; if the gap is slight its still .455.