Ok, thats probably enough photos, the compliance plate must have been broken off at some stage.
if your certain its a 50Hp its going to be a 86 - 90 year model,
the reason I am certain of that is that its a 3 cylinder engine and going off the mercury / marina serial numbers they are the only years where they were a 3 cylinder, however if its a 60HP then its a whole different ball game, with any luck you may be able to get a book on the outboard that covers this and you should be in business
I have attached them below this maybe you might be lucky enough to find one of these numbers stamped somewhere on your motor.
Good Luck with it..
Regards,
Nathan