Rinker 206 Captiva performance question

[sabre85rdj]

I bought my brothers 1990, 206 Captiva with a Yamaha sterndrive that looks like new.  Originally, it had a 5.0 liter V8 engine but my brother got a super deal on a new 5.7 liter project engine from Mercruiser in the late 90's.  He's estimating the engine is putting out in excess of 310 hp but there's no way to verify that.  I'm running a 5 blade 13 3/4x20 prop and I can pull 58 mph according to the speedometer at 4700 rpm.  My brother said he's had it over 60 mph but the hull became unstable so he had to back off.  Even at 58, I can feel the hull start to rock from side to side like it's tipping in the keel. 

I'd really like to update my engine to a throttle body fuel injection system and I was wondering if anyone has made this conversion?  The engine has been getting harder to start recently and seems to flood easily.  I could rebuild the carb but I'm thinking a TBI system could help with fuel economy and startability.  With gas at almost $4/gal, I'd like to stretch my play time.

I'm also wondering what the best prop would be?  I'm thinking about going back to a larger 3 blade prop to help get a little better launch pulling a skiier.  I tried a 14x19 aluminum prop over the weekend and lost 5 mph and had less pull out of the hole with a skiier.  Is there a better way to figure this out without having to buy a bunch of props and try them?

[DBOMB]

try a 21p 3blade mirage plus stainless it worked on my 89 206br

[frodo13056]

I had an 88 206 cuddy with the Merc 350 / 260 HP with an Alpha One drive. I had 2 stainless props that I'd switch out depending on if I was cruising or pulling skiers / boarders / tubers.
I had a 21 pitch 3 blade Mirage and could run right at 55 (GPS) all day long and the boat never felt unstable to me - of course I wouldn't run that fast if it was really choppy out. I also had 19 pitch 3 blade Mirage that I used for pulling water toys (better hole shot, less top end) and could top out at about 50 with that prop.
I also used a Stingray stainless hydrofoil - seemed to produce minimal drag at top end but added a ton of performance when pulling folks around and at lower speeds.