I am not sure what it is worth but not having a Conn mouthpiece is going to make any if little effect on value. Mouth pieces are somewhat disposable anyway. As a general rule the mouthpieces that come with horns are rarely really useful anyway. I am not a fan of selmer metal mouthpieces but may think they are great. It will give a very bright sound. It is a low pitch so that is great. If it is in alinement and with good pads you should be able to play it with no problem as a clarinet player. If it is not then a repad etc will be needed. Try a medium reed to start but try to buy a variety. Mouthpieces are very personal and horn related. A mouthpiece that I like on my French Dolnet soprano is Rico Metallite mouthpieces. Try a few different ones. That mouthpiece is a bright tone like a good metal but is in the under $30.00 range. But keep trying different combinations of stuff until you find one you like. If you have a band director or other person you know who is a sax player talk to him. Enjoy. Welcome to the world of vintage horns.