imn looking for fighters who were never great but beat (more than 1) great fighters when they were young close to peak
Randy Sandy Well good might be a stretch there, but proof you could still wrack up some real nice win sin that sort of fighting environment even if you are losing 8\9 out of 10 to ranked opponents.
Don Williams had multiple wins over HOFers (Lew Jenkins, Ike Williams, Bob Montgomery, Sammy Angott) but I'm not sure how many of them, if any, were still at their peaks. Andy "The Hawk" Price beat both Carlos Palomino and Pipino Cuevas shortly before either became champion.
If you have a flexible definition of great then Robbie Sims applies. He beat Duran and Barkley. Some will say Barkley wasn' great but the fact is that he was a three division titlist.