RE: Small diameter props and large spinners
Yes you'll loose some thrust but not as much as if you mismatched a smaller spinner to the larger front of your fuselage.
Yes it will cut down the drag on your Corsair.
Try larger diameter lower pitch props too you'll be surprised at how fast they can be on this type of pylon racers, they accelerate out of the corners better and by the time the high pitch proped planes catch you, well they won't you'll be through the next corner by then....