This engine oil should work for you....
http://www.harley-davidson.com/gma/gma_product.jsp?PRODUCT%3C%3Eprd_id=845524442090723&FOLDER%3C%3Efolder_id=2534374309041089&ASSORTMENT%3C%3East_id=2534374309041089&bmUID=1218570025367&bmLocale=en_US
I've used ot some years in my Norton 16H
Sven
Classic Oil Supply in Richmond, Va. U.S.A. sells Morris oil and they have what you need. 804-261-4140, if he is still in business. I have purchased from him but have no other connection.