I have an Oscar with 2 Severums. They mostly get along quite well, these days -- residing in a 210 with a Juripari, a Pleco, and a TSN. In fact the O and the Green Sev are "best buddies". Tank size does matter, though. They grew up in a 55, and when the O got to about 7" started chasing the Sev pretty ferociously. The big tank really relaxed everyone, and aside from normal cichlid rowdiness everyone is getting along fine. The 72 might be enough tank, but also might not.
