The 6 volt starter and the 139 tooth flywheel is the correct combination. A 168 tooth ring gear is used with the 12 volt (red label) starter. Both starter drives have the same number of teeth, but the angle of the 12V teeth does not match the spacing of the 139 tooth gear. It is impossible to interchange the 6V and 12V drive gears because the shafts are different sizes, and there are other physical differences.
The foot linkage simply engages the starter drive gear mechanically, and then closes a heavy duty switch on top of the starter to spin the motor. The key switch supplies voltage to the ignition system and other accessories and it has nothing to do with making the starting motor run.
Jerry
