Tigerdude,
Reducing the propeller size isn't always good thing to consider here. Reducing the prop size reduces the thrust put out by the engine which reduces the power output of the engine. Plus, if you put a too small of a prop for the engine you can ruin the engine. Adding larger wheels doesn't add that much weight to a plane at all, maybe a few ounces which isn't nearly enough to affect the flight of a trainer.

Ken