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..