The Single Six is made in .32 H&R Magnum. And the guns are the same frame. If you can get your present cylinder bored to .32 H&R, the rest is faily easy. All you need to do is get a centerfire firing pin assembly and replace the rimfire firing pin assembly.
You have to disassemble your Single Six to remove the loading gate to get access to the firing pin retaining pin and drive that out:
I used a long steel rod, wrapped in tap, to set the new assembly:
When removing the firing pin, place a piece of tape over the firing pin bushing, as its spring loaded and will fly out when released.
Otherwise, the job is simple, if
you're handy with tools.
Excuse me ~ I got called away before finishing.
Ruger won't sell you a barrel, but many custom gunsmiths have take-off barrels they're willing to sell. Replacing a barrel is far cheaper than re-boring one. Barrel replacement is not exactly rocket science, but does require a good set up.