RCU Forums - Getting the old girl back on the water (hydrospeed Graupner from the 80's)

Hi, this was the boat I had as a kid... she worked rather well back then on the original Graupner motor and prop system with the then modern vario.
Now as she has stood up to the time rather well I am looking to get her back on the water, this time for my kids.
So I'm going to gut her and replace the broken rudder system by an aluminium prop/rudder a flex shaft, new prop, brushless motor (water cooled) and probably powered by a 3s lipo.
My question is what size motor and kv and prop to pick so I have a decent speed and a good run time.
PS the mah of the lipo battery will depend on the space I have left to fit the battery in the boat which will then also determine the run time.
Any advice welcome.

Lol similar to the Graupner system boat from the other thread... lol must that time of year lol

Hope to attach some pics later when I find them