In the second diner scene there is two men sitting at the counter that are drawn as Christopher reeves and pepper martin the man who assaulted superman while he was powerless in the 2nd original superman film.
Basil Karlo was the first comic-book Clayface; his first appearance was in DETECTIVE COMICS #40, June 1940 (script by Bill Finger; art by Bob Kane & Jerry Robinson).
In the diner scene, as well as the two men from Superman 2, Lois Lane and the man who lifts his plate at the end of the scene are also there.
Basil Karlo's speech in "Revenge of the Atomic Clone" echoes one by Bela Lugosi in "Bride of the Monster": Dr. Eric Vornoff: My dear Professor Strowsky, twenty years ago, I was banned from my home land, parted from my wife and son, never to see them again. Why? Because I suggested to use the atom elements, for producing super beings, beings of unthinkable strength and size. I was classed as a madman, a charlatan, outlawed in a world of science which previously honored me as a genius. Now here in this forsaken jungle hell I have proven that I am all right. No, Professor Strowski, it is no laughing matter.