Well, you say it's meant for Sp480's, that can mean a lot. I am not familiar with the airplane you are talking about, but the motor recommendation I'd give would change a lot depending on whether it was meant to be flown direct drive or geared.

On direct drive, you'd spin a 5-5" prop and maybe 7 or 8 cells. If it was geared to maybe 3:1, we are talking about and 8-5 or so and carry the weight of 8 to 10 cells. Big difference in airplanes and how they would fly!

Dave