If you get a chance, try it on a lightweight 12 foot aluminum . I am about 180 lbs and my 7.5’s will just get me on plane in my tinnie.Maybe I should try the 5.5 prop on the 7.5’s.
The 1954 Super Fastwin 15 horse will probably get your Livingston on plane.
Up until the mid eighties, outboards where measured for power at the powerhead. After the mid eighties it was measured at the prop. A "modern" 10 horse is roughly equivalent to an older 12 or even 15 horse, unless you are talking about older Mercury outboards that had under reported horsepower from the factory.
The Livingston looks like a real solid and stable fishing platform.