Roy, a small caveat. If the existing nut is tight on the thread, removing it will tend to tighten the kickstart spring retaining bolt..part 87. This is fine. But if the new nut is tight on the thread, it will tend to grip the bolt and loosen it as you rotate the nut...a bad thing. Ideally the new nut should spin easily down the bolt thread and nip up nicely, without disturbing the bolt. As described it is just an added locknut for the bolt.
It's nothing to do with part 61...these four studs have the reduced size plain and awkward hexagon nuts, part 106, but difficult to see from the diagram.
Swarfy.