Does anyone know the size of the steering wheel retaining nut and where I might get a new one?
Who are you calling a steering nut? 100Hp's are supposed to be driven like that...
If you use the right socket (preferrably hexagonal) a breaker bar with a looong extension on it and get another person to hold the steeringwheel (don't use the steeringlock), The nut should be reusable.
gr J