In Adventure #290, Sun Boy made a guest appearance in the Superboy story. But it was a major sub-plot of that story that was recycled from an earlier Superboy story in Adventure Comics. Here's page 2 from Adventure #290:
And here's the second page from Adventure #191 (99 issues or a little over eight years earlier):
As you can see, the artwork is different, but the dialog is virtually copied word for word. In both stories, the other Clark Kent attempts to steal a bottle of milk from the milkman, who recognizes him and wrongly assumes that he's just saving him a trip to the Kent's house. In both stories, Ma Kent lets him into the house and tells him to get ready for school. On the way to school, in both stories Lana Lang tests Clark to see if he's Superboy and learns that he's not invulnerable. And in both stories, the new Clark learns Superboy's real identity, and is reformed.