I understand fully. When I got my tumblers out of whack I thought at first I would have to tow it to the HD shop. I stupidly turned the ignition knob without first having the washer/spacer/nut assembly in place to position it properly at the right depth.
To fix it I just looked at the shaft and rod, then with a flat-blade screwdriver matched the tumblers up with the rod. It was a tense moment but it worked, and I won't make the same dumb mistake again.
Anyway, the Parnes tool does the same thing as inserting the ignition-switch knob, with the spacer assembly in place of course. With the tool you don't need that.