I'll assume you have a New Model Blackhawk, eh? The hammer and pawl are in the "at rest" position and you either have the type of pawl that cams to the rear (current design on several models) or the upper tooth is shaved a bit so it "just" clears the ratchet.
Now, the Old Army loads/unloads off of half cock. The only possible way to get the pawl out of the way of the ratchet would be some sort of cam system, however it would have to permit the pawl to snap back into position as the hammer is moved from half cock to full cock, engaging the ratchet and then rotating it to the "in battery" position. So, I have doubts that'll work........
JMHO,
flatgate