I have a 54 3.3hp, it is not to much different than you 49. I run TCW3 synthetic oil at 20 to one and it does fine. Those automotive oil that they used to recommend made carbon in the exhaust build up like crazy! Synthetic oils are better for the water we play in and we should all remember that. Big controversy on this website about oil and the ratio. Your old motor has no ball bearings of any type. The thought is more oil is better. My humble opinion is, extra oil just goes out the exhaust.
dale