The model # is located on the port side of the transom bracket. It is also located on the engine (block), not head, in the shape of a freeze plug, NOT a freeze plug ! It's about the size of a nickle. It could be silver or painted. 40502, 40503, 40562, 40563, 40572, 40573 would indicate a 1965. Find the # and I'll let you know what year it is. The owners manual states a 40 to 1 mix ratio for early 65's but 50 to 1 of TCW-3 will be just fine. That's 1 pint to 6 US gallons of gasoline. If I'm not mistaken your 40hp was equipped with the charging kit. I know that the smaller engines were not, in the rope start.