RE: J-3 cub Identifly.
Well I am a plane, helicopter, car, boat kind of guy.
Common sense makes GOOD motors.
You are looking for a motor in the range of 35mm dia by 42mm long Length can go to 48-50mm with a KV rating of 900-1100KV weight around 140-160 grams.
Higher KV smaller prop, lower KV larger prop.
That should put you in the ball park.
Buzz.