Only a pair of dwarf pike cichlids, in that limited size tank.
It would probably work with Walliciia (aka Crenicichla) compressiceps, notopthalmus, or regaini.
There are more in genus (8 Total), but the 3 above are most redly available.
Since these are often found in the same waters with Heros, and since they are totally different in shape, they would probably work until they outgrew the tank.
I have also kept pike cichlids with Guianacara, and there was very little competition, because of their dissimilar shapes.
And the Guianacara probably wouldn't out grow a 75, like many other S American cichlids.
My other tank mates choices would be non-cichlids, such as geographical lycorrect, and large enough tetra species (Characins).
Too many other cichlids usually mean competition for space and resources, whereas non- cichlids, if not small enough to eat, are often ignaored..