These reprints had a bit of a purpose, and this incredible cover was just the beginning of new happenings in the Superman titles.
But, first, the stories contained within the Giant....
Superman had to find his way around, being mistaken for an extra on a Kryptonian movie set for "The Space Explorers", meeting his parents, Jor-El and Lara, on the day they were married and attending the ceremony, then going to work for Jor-El as he attempts to save the inhabitants of Krypton from the upcoming explosion with a fleet of space arks.
Adventure Comics #313
Still, it was quite an adventure for the Boy of Steel, after making a gift for Pa Kent, young Clark Kent went to the Mind-Prober Ray to learn of how Father's Day was celebrated on Krypton....and that each Kryptonian house had a fortress with statues of their ancestors, which Kryptonians were suppose to honor at a certain age.
Superboy had ended up on Earth before this happened, so he had a little extra mystery to solve, as well as being tormented by Jax-Ur, a Kryptonian criminal from the Phantom Zone, and, the fact that, while he found the statues in space, they had been turned to Kryptonite! Still, Superboy did beat these obstacles, and discovered more on Val-El, Sul-El, Tala-El, Hatu-El and Gam-El.
Kryptonian criminal Ras-Krom escaped from the Phantom Zone after the detonation of a nuclear bomb. Disguising himself as "The Old Man from the Cosmos", he tried to steal nuclear weapons to open a rift to allow the rest of the Phantom Zone villains out, but, while fighting Superman, revealed his fear of ancient Kryptonian superstitions, which allowed Superman to herd him Ras-Krom to where he needed him to be, to nullify a device the criminal created to prevent Superman from sending back into the Phantom Zone.
Adventure Comics #216
Well, there is a team-up in the story, but it was Superboy getting help from a professor that had been lost in the African jungle, looking for a meteor that had crashed there. That meteor was the remnants of a Kryptonian city, so Superboy couldn't go into the area, as it had been turned into Kryptonite, so he dressed his new pal as Superman, to confuse Vedders, the guide who abandoned the explorer to another city, that of ancient knights, who had gotten lost in Africa. Superboy helped the new "Superman" to defeat Vedders, bury the city to keep others away from it, and take the lost knights to civilization. Then, Superboy was able to reunite the explorer with his son, Jimmy, who proclaimed Superboy would forever be his pal for finding his dad, Professor Mark Olsen. Shame Jimmy was too young to get a picture of the occasion....