Mercury Force 40 or 50HP

[ozforce]

In the absence of a serial number, how do I determine the difference between a 40HP and a 50 HP on a H050412SD [ELPT]. I know the carby is different in the jets but that is all I can find.
The reason I ask is because I suspect my motor has the wrong engine cover fitted.

 

[Faztbullet]

You half there...the carb venturi is smaller on a 40 and high speed jet is different, This is only difference..