as far staying within any school of design,......
i'd say it's pretty hard to assume that any particular school hasn't been built with an alternative, or "outside the norm", wood for a stock at some time or another. I think the gest of the term "school" has more to do with the gun's architecture and specific component design than specific wood used for the stock.....as long as the wood used is at least, an "accepted stock wood" (and ash has been used many times), the gun is true to origin.