I have a 65 Mercury half ton with the 240 and three on the tree. It’s still sitting out on the farm - I’d love to get it out to B.C. lots of fun driving that one around..,I owned a couple of the 300/6. All mine came with the NP 4 speed. That engine came out in 1965 - along with the 240 - well outside my 40 year window.
I did not choose 40 years randomly.