I have a 1987 Evinrude 2.5hp with a factory saddle or ‘pannier’ tank. They made a 4hp vers I need of this motor too. I’m not sure if this could work with your motor or not, but the tank itself is pretty small and handy by itself. They aren’t real common pieces to find by themselves and I have seen a fair number of these motors without the tank. This is a picture of the saddle tank anyway, so you can see what it looks like.
-Ben
OldJohnnyRude on YouTube