If you want "singles", 12.5s would be good radials to run, but remember they are a tad shorter than stock 900x20s. The good news is you can still use your deuce rims.
If you want "super singles", you need to find a wider AND taller tire. Go with some meat like SpicerGear and me. 15.5s or 395s seem to be a good choice. They are 15.5" wide and 46.7" high. Your gonna need new rims or modify your existing ones. There is always a catch!