As I recall Mercury made 2 cylinder 20 hp engines that outran everything in their class and the classic 40 HP which a friend of mine had, and later the 30 hp 4 cylinder of which I had one on a used boat I bought. All support what I said.
Edit: Recalling their green, clamshell cowl, gray LU, I recall their 25 in their early days....that was before my boating experience days...Oh and my FIL had a '58 Rude. Thing about those 2 cal. OMCs is that they had soft engine to clamp bracket rubber mounts so that the engine could shake back and forth when idling (alternate firing twin) and not shake the boat. When PT came to being they had to toughen up those mounts. I had a '58 18 HP Rude I bought later