Slowly I'm getting the parts for my first boat (scale) and I need help with finding a U-joint for my 550 motor.
I have installed a gear box 2.5:1 ratio to slow down the speed. The problem that I have is the output shaft form the gear box is much larger than the prop shaft and I need a U-joint that has different size holes. Here are some info since I don't know the shafts sizes:

-motor and prop shaft from a Great Planes Stinger boat.
-gear box from Great Planes model GD-600

Attached are a few pics of the parts.

Thanks.