I considered this further and am pretty sure there were no juniors, or for that matter adults, who I thought of by nicknames. They would come to mind as first names or surnames or a mixture of both. I think this was general among adult players in the 1960s and 1970s, it wasn't a nickname era.
Nowadays everybody knows who is meant by Spess, Mondo or Nosher, but that's probably a function of the Kingpin/Private Eye age. The only parallel I can think in the former period is that in the late 1960s when they were rivals Hartston and Keene used to refer to Basman as Batman. Of course it's entirely possible that juniors in the 1970s had nicknames for each other that I wasn't aware of.