For a Kadet? Any .46 sould be more than adequate. I've seen them take of grass fields and do adequate basic aerobatics with as small as .29. I think they were originally sold to be powered with .25 to .40, back when flight packs were more than twice as heavy as they are now.
I passed my club's solo flight requirement on a Kadet Mk II lent to me that was powered by an older OS Max 35, that was definitely NOT a powerhouse. No trouble getting off our grass field.