Barrel swap on 1970 OM Blackhawk
So I have a 1970 OM Blackhawk .357/9mm convertible. It is not converted and it is the 3 screw model (was told these details mattered). It has the shorter barrel, 4 7/8 inch I think, the ejector port is flushed with the barrel if that means anything. I like the look of the 6 1/2 inch barrel and was wondering if it is worth the effort to have it changed out as well as the cost. Would the cost be so significant that I should just keep this one as is and just go buy another one in the barrel length I want? Lastly, if I decide to, is there a difference in the .357 and the .357/.9mm barrel? I have found a few barrels for sale but they are listed as OM Ruger Blackhawk .357 and when I asked if it is the same as the convertible, I get crickets.