I have one of the .45 Colt SS Bisleys. One or two limited runs. 5.5" barrel. Also made a run of .44 mag. Very nice.
I don't believe Ruger made a SS NMBH convertible, but they did sell and fit a spare .45 ACP cylinder to an SS NMBH. I had several SS NMBHs rebarreled from 7.5 to 5.5", with .45 ACP cylinders. Call Ruger to see if they will still do it.