From Adventure Comics #363, the ultimate crossover event of the 1960's:
Super-Turtle popped up a few times as filler. This was about as funny as it ever got.
Then again, this is as entertaining as Superman ever gets, so there you go.
Meanwhile, I never knew this:
and I have to admit, it answers a lot of questions I never even thought to ask.
From the letters page:
Fair question. I'm not sure who the next new member of the Legion was going to be, because Tyroc wouldn't pop up for years. I'll let you know when I come upon him/her. I'm pretty sure it wasn't Luke Cage, because that would have caused the universe to collapse under the weight of all the awesomeness as he beat the crap out of every guy and slept with all the girls.
You'd totally buy a Luke Cage and the Legion of Super-Heroes series. Don't try and tell me you wouldn't.