Hello, several years ago I bought the plan of the Jupiter hydro from the US and built a 152VO Jupiter. A friend who saw it running suggested we build two of the real full size ones, one each. So eventually three years ago I built a full size Jupiter. I wanted it to be totally authentic so I bought a 1954 Mercury Mark 20H, the engine that was generally mounted on the Jupiter in B Class. I had to import it from the US, they are extremely rare in France where I live. I have been running the Jupiter two seasons now, fresh water only. Top speed so far is 39 knots, or about 72 km/h. I think I should be able to reach 80 km/h but it's very delicate to adjust the trim, height of the engine and angle, and also the weight is very important.
If anybody wants to try, building a Jupiter is not very expensive, and there is no need for special tools, but one has to be very meticulous and precise. A good model builder can do it.
A few pictures of my full size Jupiter. The small one is registered no 184.