I would use Mercruisers prop calculator to see what it recommends.
More blades equates to a better bite in the water however that also means less slippage for a holeshot so the engine will be slower to rev. A 4.3 should have enough torque but you will need to pick a prop with the right pitch and diameter to not overload the engine.
1997 2400 SCR
5.7 Vortec / Bravo 2