Thanks for the answers. When I saw the picture of the breech end, I remembered my books weren't all boxed up from the fire and I had the info all along.
I walked in a pawn shop, hopeing to see a blue gp100, only to find a OM Single Six with a 4 5/8 barrel. I asked if they might have the lr cylinder that goes with it, and got reamed a new one from the sales lady. I was told that it was only made as a 22lr, and no mag cylinder could be had.
They were asking $325 and I offered $200. We agreed on $250otd. Now my quest for the lr cylinder.
Sometimes the worm eats the bird.