Hi!
I agree with "Buzzard Bait"! Too big engine in a trainer is no good!
Been and instructor for 40 years and seen many newcomers with too big engines in their trainers getting in trouble just because they have too powerful engine up front.
The SIG cub would fly just fine on a OS .LA .40 swinging a 12x4 prop. A .70 four stroke is just to powerful!, At least if you fly at sea level.