RE: MHZ Mystic cat
MHZ is offering the Jetcat's as an option so I'm guessing they fit and have mounting brackets.
This would be a great project if you're comfortable with boats to the point that you know what to expect and how to keep it right side up.
This is the direction I intend to head once I'm comfortable enough with RC boats.
I agree with the used RTR given that you see it run personally first.