Binder, Swan and Abel conclude the Anti-Superman Gang’s plans in Action 377 (June 1969).
To get away from the kryptonite-spewing satellite, Superman flies down and into the Earth. He finds more lead, and makes another suit. Once again the Gang uses the element-changing ray on it, but this time Superman follows the ray back to its source.
There, the Anti-Superman Gang captures Superman, using more kryptonite, and stick him in a kryptonite cage. Superman bursts free, claiming to now be immune to kryptonite. In reality, he is just wearing a flexible lead-glass outfit to protect himself.
Flexible lead-glass. Yeah. Ok.
Although the Legion of Super-Heroes series technically begins with this issue, the story is a reprint of their first solo tale, from Adventure Comics 300.