Cimarron carrys some factory conversions.
www.cimarron-firearms.com/conversions.htm
One of the gun rags had an article a year or 2 ago about conversions, their legality and where to buy them. I don't recall offhand which magazine it was. NRA American Rifleman comes to mind, but I'm not sure. I've looked real hard at that R&D setup and an Old Army...looks nice but pricey.