ORIGINAL: rio 51 racer
So which of those motors is best
That's the age old question to which you are unlikely to get a definitive answer, it is all opinions. All the motors you list are able to get the Rio to (and past) 50MPH, but the speed is in the set up, my advice would be to try and steer yourself away from speed targets, rather start to try to get the model running reliably first, new motor and drive line, then the steering hardware and I know some end up refitting the radio gear.
Then, as your boat gets better and you work out the set up, the speed will come to you but hopefully a nicely handling hull will evolve with it. I have had 50MPH plus boats in the past that were a real pain in the neck to run, often they would be doing 50 upsdie down and 6 feet above the water - no fun, but I learned the hard way I guess.
If it were me in your shoes, I would look for a good used motor to get you going, plenty about.
Zenoah, RCMK and Quickdraw are all good motors with easy spares availability, I'd be looking for a used one of these motors.
As Scott Schneider said though, doing as much work as you are proposing to, you might be as well to build yourself one up from scratch.
Glenn