To me, the prop seems to be a good choice. It's even "scale" in diameter and the pitch/diameter ratio makes it efficient. The motor is just a too low Kv type that would deliver far too much power at a cell count needed to reach 65 mph flight speed (80 mph pitch speed). Motocalc is not needed to see that. I'd rather choose a 380 Kv motor and 5 or 6 cells. Power/weight ratio could be as low as 0.45 and would still give take-offs like an unloaded original.