Gentleman,
It is a USFA "Gunslinger" model (I hate that name) and is made of all USA sourced parts, i.e. one of the good ones. The 58,XXX serial range is correct for that model. I know because I have two of them. One is a black powder framed 7-1/2" 45 Colt. The second is a 4-3/4" smokeless framed 38 Colt and Smith & Wesson Special.
When I first read about these I thought it was a dumb idea. When I actually saw one I was completely taken and bought the first one I came across (the 7-1/2"). I was told, I believe here on CASCity, that they didn't just leave the guns in the white to rust, rather they came up with an actual finish that gives the vintage appearance but doesn't continue to rust. The two guns I have have stayed in original condition with no futher rusting. They do show a little holster wear in all the usual places, making me think it is an actual finish as I was told.
Dave