Necking down does not work well in the revolver format. <Please don't respond with the various necked wildcats as it has no bearing here since the cylinder is cut for them> If you say take a .327 fed case and neck it down so it will slide all the way into the cylinder, when you fire the case it will set back against the breech face and the case will expand to fill the gap the moving back has created. you now have a stuck case in a revolver and you cylinder will not revolve. I'd done this so many times in 38, 41, 44, and 45 and just have never found a way to get around it, short of re-chambering the cylinder.
#12 shot works great for just about anything you would shoot with shot loaded revolver, snakes, rats, mice, etc. I've seen a .45 ACP loaded with 170g of #12 drop dove and pigeons like crazy. So many folks poo-poo #12 that I can only assume they either do not have real experience with it or are using it beyond its capacity.
About the only thing I would really suggest for the .32 H&R is a very light load of fast burning pistol powder (bullseye, red-dot, AA#2) a gascheck pressed into the case all the way onto the powder and slightly compressed and see how much shot you can get. You will need to do a little experimentation to figure out what your load will be, but it should work okay.