take the weight of the plane ready to fly. this should be easy to find with a quick Google search.
I like a 1:1 or higher thrust to weight ratio another thing to consider is if you need to add lead if you need lead in the nose, might want to run a larger motor/battery combo and then underprop it. at less then a pound empty, id guess a 400-450 class motor. if it were me, id probably just throw a 450 sport on it from www.headsuprc.com
with a 30 amp esc, 10x5 prop and 1800-2200 mah 3 cell. pulls about 38 oz of thrust. this may also depend on your prop clearance though. if you only have enough room for a 7 or 8 inch prop, you might want a different motor or battery.