I have that very gun. It's a Sweet Sixteen I purchased (my first) in 1966. The finish was likely a poly urethane and was high gloss. I have seen old refinished stocks (with shellac type products) that turned yellow and peeled. I'd just strip it down, sand thoroughly and refinish with urethane. Allow complete drying between coats and rub with very fine steel wool. When done, apply a light coat of wood polish or wax and you'll be good to go...IMO