There are two potential problems using the .32-20 in the .30M1 chamber. One, headspace may not be correct if you headspace off the rim. If you headspace off the case mouth you might be all right, with the caveat that the .32-20 brass is very weak compared to .30M1 brass.
This leads to the other problem. None of my revolver chambers have a deep, sharp step at the case mouth like the .30M1 chamber has. This means that the .32-20 bullet will likely be shaved as it passes over this step. Even cutting the case to headspace on the step will not solve this - the .32-20 case is very very thin, and the .30M1 case is very thick, so the .32-20 case may lie at the bottom of the chamber and not be centered in the chamber. This would point the bullet at the bottom edge of the step, with bullet damage a possibility.
OTOH this may work very well. I don't want to discourage you, just keep you appraised of the potentials for trouble. Make initial tests with low pressure loads and have fun.