Name:   GoneFishin - Subject:   Prop Recommendation Date:   4/7/2022 3:58:54 PM

Here is some info on  the engine. The reference is to a 1989 but what is important is it's a card engine like yours. Enjoy your boat.

https://www.justanswer.com/boat/diw4q-1989-mercruiser-4-3l-gmc-two-barrel-carb-starts.html

I have never used a 4 blade....I assume you have a 14x21. I suspect since you want to pull a 240lb  skier a 3 blade gives you more  low  end. A 4 blade will give you more top end.

Have you  checked the Merc Cruiser table  for   correct prop?