paul my valiant had a suzuki 70 4t on the back which was fine as its rated up to 80hp . I always felt a lighter 75 2 stroke may have suited it better but at the expense of much more fuel,unless you can find one with an etec
6k ish should get you a really tidy valiant about 2001-2 , they are fine for family fun use and mine had no problems at that age ,
the ribcraft or searider are certainly better quality and probably better sea boats but lots more money and the ribcrafts usually have a 50
What about the smaller humbers ?