UPDATE
The crayfish handled its own to say the least. On it first day it messed up a large Jack Dempsey pretty good.. actually thought the jack dempsey might not make it for awhile. From what I saw, it had zero problems with the eel during the week or so it was in the big tank.
I decided to move it to my smaller 72 bowfront 2 days ago because he really was getting too aggressive with the other fish. He didn't kill any but as I observed, he reminded me of that bully from elementary school lol... even when he wasn't physically harming the fish, you could tell they were visually stressed out around him.
The main problem i've encountered with the crayfish is it climbing out of the tank at night. It's happened twice already in each of the tanks.. I need to put the plastic slits on the back of the glass canopy's.