I'd suggest at least a decent 46 two stroke like the Thunder Tiger 46 PRO. If going with a four stroke, a Saito 56 would probably pull it well enough and would likely knife edge with a 12 or 13 X 4 prop.

First thing I'd try though is a 10 X 4 or 10 X 5 prop on the 39.

Good luck,
Dennis-