You can find D frame Colt Detective Specials with a shroud and perhaps a 2.5” Diamondback for your adjustable sighted gun. They are getting pricey, especially the Diamondbacks. Not sure I’d mess around trying to convert the older Colts to DAO. You could also do a S&W Model 10 and a Model 15 in 2” versions, but neither will have an enclosed hammer. You could bob the hammers and make them DAO pretty easily. They would be my choice. A Ruger Speed Six and a Security Six with 2.75” barrels and spurless hammers?