The very simplest way to have a 32-20 Vaquero is to start with a .32 H&R Mag 'Vaquerito'. This is the same size as the single six with fixed sights. Below are my two 32-20 conversions. the 1st is the adjustable sight .32 version, but either frame will work. It's actually a better size frame for the cartridge. The mid-size New Vaquero and large frame original Vaquero are way oversize for the 32-20 IMO.
The 32-20 cartridge pressure is well under the 32 H&R Mag that the Rugers were designed for so a very safe conversion. All that is required is reaming the chambers with a 32-20 finishing reamer from Brownells that I did myself by hand. You can use the original cylinder or obtain an extra cylinder on Gunbroker. They are easy to find and under $100, sometimes as low as $50. I bought an extra cylinder and made my 32 single six and Old Model 22 singles six 'convertibles'. Yes the single six cylinder is a little short. So reloading helps.
I shorten some cases and reload them or I use factory loaded rounds and simply run them into my seating die to push the bullet deep enough to fit the cylinder. The 32-20 cartridge has more case capacity than needed and actually becomes a more efficient cartridge with some of the extra, unused case capacity reduced. Both long and short versions feed well in my .32-20 Winchester '92 companion rifle.
Here's my new model .32 H&R Mag:Bisley hammer, with modified spur, Stainless Steel grip frame, steel ejector rod housing, SBH grooved trigger w/web removed, Colt ejector rod, and free-spin cylinder pawl. I reamed the original 32 cylinder to 327 Fed Mag. And a another to 32-20.
And here's my old model. After converting the frame to center fire, I reamed one 32 H&R Mag cylinder to 327 Fed Mag. And since then added another reamed to 32-20.
On both guns, the loading chute had to be enlarged slightly for the larger rim diameter of the 32-20: