The feeler gauge is a good idea.Yes, although the plastic piece is not necessary, I use a feeler gauge bolted to the stud, and just bend it to contact the body of the mag to ground it out and shut the bike off. The voltage is so low you don't feel it.
The little red plastic push in button that comes on the kill tab will fall out sooner or later, and when it does, you don't need it. Also, you're going to have to run solid core plug wires, not the carbon core ones. I learned that the hard way. Mine would start with the carbon core wires but they stopped working at a higher RPM, leaving me stranded. Took a while to figure that one out. I said, "This magneto is a piece of shit!", turns out I didn't know what I was doing. Live and learn.