In 39/40 that O&R would have been an ignition engine with a movable set of pointe[ it moved to retard the timing for starting and obviously to advance it to get power.
If it dosn't have them and there is a factory cover over the area where the points would have been then it is post war. Also the pre war might not have had mounting lugs as a modern motor has
I only had post war models as I'm ...well post WW2 era. By todays standards they would be woefully anemmic powerwise, a good Norvel 074 or OS LA 10 would make as much power as it had. Still they were decent runners until surpassed by more modern stuff if you can call the Fox 35 [1949] modern.
So are you selling this critter or giving it to some lucky person.
Dennis