As stiker, noted, a male N. tetracanthus will be quite cramped in a 55 close to adulthood, and has the attitude and capability to do damage when put in a "too small" tank, especially with a similar shaped, competitive looking cichlid, like a Crenicichla. A female would fit better in the tank, reaching only 2/3rds the size of a male, but body shape, mouth shape, other similarities usually don't bode well when combining two cichlids in a confined space.
And Cuban's being the only cichlid in their natural habitat, "often" do not play well with other cichlids in community settings
I have kept both cichlids you are considering, and found a 125 gallon minimum tank size I would use.
female Cuban above
The shape of A cutteri, would indicate it might be a better choice, being quite dissimilar in body and mouth type, so less chance of being perceived as a directcompetitor.
Although ..... IMO cutteri also get too large for a 55.
Male cutteri I had above, larger than the size of a kids football.
A better choice, size, attitude, acceptance of water parameters, and shape wise might be Guianacara, topping out at reasonable size for a 55 gallon, and being a geographically correct resident of habitat in South America. South America has much more diverse communities of cichlids, living together, making them more tolerant of communal living situations than Central Americans.
