Saving Old Seagulls

Hi All,
I’ve just picked up a 4hp Seagull Sport, I see from the spec sheet that the 4,5 and 6hp models have identical specs and weight apart from the integral tank on the 4hp although it was an option on the 5/6 hp models. How would I upgrade the 4 to a 6hp? Ignition? Prop?

Any info would be great
Thank you

It's dependant on exactly which model you've got, the number's on the side of the cylinder.

A pic of both sides of the power head would help.

Hi, I’m picking up the motor this weekend so I’ll take sone pics,
Thank you