The entire distributor moves for vacuum advance on the stovebolt engines. Below the breaker plate, there is a set of centrifugal weights, so the cam assembly moves to advance the spark from engine speed changes just like a V-8. It's possible for the stud that goes through the housing to get grounded, creating the same effect as the points being closed all the time- - - -no spark. That's why it's important to get the points open, and then check for voltage at the terminal on the outside of the distributor housing. With the points open, voltage will go all the way to the insulated point so full battery voltage will be measured at all connections from the battery to the insulated point. There will be NO voltage differences anywhere in the system until current starts to flow when the points close. It's like pressure in a water hose being the same all the way to the nozzle until water starts to flow. No flow- - - - -no pressure drop.
Jerry
