Depends on the lion too. I wouldn't recommend a volitan for an extended period. I had about a 14 inch one in my 200 and he wasnt fully grown I believe. They would live for a while in the 80, it would be pointless though cause they would be so stressed and unhappy.
As far as eels, same thing goes. Depends on the eel. But, they tend to be a little more tolerant of smaller tanks because they like to hide in the rockwork anyways. I had about a 4 foot tessy eel in the same tank with the lion. They did well together. But, I don't think he would be too happy in an 80. A nice snowflake, or similar passive type moray might be nice. Tessys are vicious so careful of them. Beautiful though.
And nix on the shark. Nada, no way, no how. Inhumane. You in a jail cell for life basically. Good luck with the others though.