Since you're leaning toward the 20 ga. this appears to be a good buy. Unfired, in the box and some nice looking wood.
http://www.gunbroker.com/Auction/ViewItem.asp?Item=124057280Plan on making a strong loading, cleaning rod. The ramrod that comes with these is usless. My loading routing for many years has been to wipe with a damp patch after EACH shot, using flannel patches slightly damp with moose milk. This makes every shot load as easily as the first one. It is also a good safety practice, making it unlikely that a glowing spark will remain in the breech. For wads, I use 1 over-powder card, no "filler/cushion/cleaner" wad. The thick fiber wad contributes nothing to the pattern and just adds weight(recoil). An over shot on top of the shot and you're ready to go. V. M. Starr knew very well what he was talking about. He's my hero. My success in loading/shooting this way has satisfied me that he was right.