I would go ahead and put a billet 2nd in it. I've broke teeth on gears before with a little 4mil small-block twister. It can and does happen. When it happened to me I also broke a set of cases (which already had a chain whack). The price of the billet 2nd isn't that bad compared to the time to tear down and rebuild with new cases, new transmission, gaskets, seals, etc. If you can afford the billet 2nd, do it.