The Civil War had ended less than ten years earlier and immediately after a war is always a difficult time to think about changing anything, there being warehouses full of firearms that would soon be obsolete.
True. Which is where we came up with the Trapdoor Springfield. Originally called the Allen Conversion, it used stocks, barrels, and some parts from Springfield .58 Cal rifled muskets, with the barrels drilled out and relined, chambered for the .50-70 Gov't cartridge.
I think you mean .32-20. The .32-40 was a long, tapered-cased rifle cartridge very popular with target shooters. I used to have some John Wayne Commemorative Winchesters chambered in .32-40, and still have some boxes of the commemorative ammo in my gun safe. It was about the same length as the .45-70 -- way too big to have ever been chambered in a Colt 1873.