These engines really don't need extra ZDDP...the level of it in '30s thru '50s oil was pretty low, and today's oils have much better add packs to prevent wear. I also would have concerns about ND oil previously being used, but it sounds like you really don't have access to that info. Personally (as the owner of a 230 myself), if it were mine, I'd pick a quality 10W30 and run it. Keep a close eye on it, and if it gets dirty quickly, maybe change the bypass filter early.