Lumpy, Eddie and Wally were the main three of the older boys. There might have been others, but mostly it was those three. Lumpy was there to be roped into Eddie's schemes when Wally didn't want to get involved.
Lumpy's dad was the only one who really called him Clarence. Even Ward would slip and call him Lumpy.
Yeah, Gilbert was Beaver's friend. And there was also Larry, who was kind of chunky like Lumpy, IIRC.
Edit: Looks like there was also Tooey and Chester that hung out with Wally and the others early on, but only Eddie and Lumpy were there the whole run of the show.
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