It sounds like an early hammer with a hammer block on the hammer. If you look under the back of the hammer spur, you will see a screw head. If you rotate that screw head 180 degrees, it will switch from rim fire to center fire. It's still not a good idea to dry fire practice with the hammer block set. It will peen over the blocking pin, and gouge out the receiver.
I hope you got a good deal anyway, but it's not anything "special" or "rare". I have 2 early frames and 1 later "easy open" frame myself.