I cannot answer you question definitively, but by the summer of 1974 the line up consisted of Russ, Kev, Richard, Keith Minshull, John Vincent and Martyn Ellis playing "oldies" in the main room.
Mr. M's wasn't open then, just The Beachcomber downstairs in the building complex, before and after the main event....and the allnighter didn't start until 2 a.m.
I hope this is helpful, sorry if it isn't.....all the best.