Use a steel paper clip. The diameter is exactly right to set the clearance between starter teeth and flywheel. You will probably need to shim it to get it just right. Force the starter end out with a screwdriver and push the paper clip (Unbent) into the gap between the flywheel and starter teeth.
The voltage thing is spot on too. If you have a bad earth or positive you're gonna find out with the starter. I stripped the teeth of a 572ci flywheel trying to start it with a half dead battery.