I would re-think the hammer gun conversion if I were you. It will most likely take some serious rebuilding to get it to where it would work safely, if ever. I once knew a man who had half of the bridge of his nose removed from a firing pin that blew out of a .410 double barrel shotgun. He had foolishly put a long shell in a short chambered gun. Luckily, it was the right side that blew or he might have been killed. It was a sidelock gun and after the blowup, the hammer on the right lock would rotate completely around on the lockplate. The gun had Floating Firing pins in it that had keeper screws that came in from the side to hold the pins in place. Like most older guns, these screws were badly worn and may have contributed to the accident, but only in a minimal way. It was going to blow up one way or another, anyway.
I know all this because he later brought the gun to me to see if I would fix it for him! I turned down the job and advised him against it being fixed to fire, ever again. Bob H.