Remove the spark plug, put the engine in gear and see if you can make the engine turn by pushing it (or turning the wheels while up on blocks). 1st is a difficult gear, put it in third if it will go. If the engine is not siezed, it will turn with the plug out.

 

Also..the way we figured it out (although we saw the gears didnt spin but just to make sure) we pop started it and it started which is a way to make sure its deff. not the motor.

 

Its good that your motor is okay. Opening up the side cover to fix the shifter is a somewhat minor operation.