Hi, your arowana will work fine with the wolf fish at that size. The wolf fish is a Hoplias malabaricus right? if so you cannot have discus in that tank, eventhough its too big to fit into wolf fish's mouth, its still a risk. And cichlids a big nono, my Hoplias malabaricus has eaten a pair of full grown convict cichlids during spawn period and a jaguar, etc....
I would recommend arowana(silver+jardini all work fine), aligator gar, and be honest, i wouldn't recommend H.Malabaricus, though it is tougher than red/gold wolf fish, it doesn't move as much and kick your aquarium hood several times every night, making you unable to sleep. I recommend rainbow/red wolf fish, they are much more active, pretty, and fun to watch. If you are getting red/rainbow wolf, try removing discus and convert your wolf fish into shrimps, then add discus because discus are weak, its one bite K.O., once wolf are converted to dead food, they won't pick on targets that are not easy to fit into their mouth.