. I would make sure there are lots of plants and chunks of wood to break up the line of sight so the fish can get well out of sight of each other.
Just be aware though that they will continually challenge each other. I have had two species of dwarf cichlid in my 70g (also 4 feeet like your 55g) and would not do it again. I believe that two of the females were in fact killed due to the continual "pushing" of the other species. Cichlids are cichlids; females can be very nasty to other females especially if they are guarding eggs and fry, and cichlids will spawn regularly. Any cichlid is going to regard such a small space (to the fish) as "his territory," and females seem to go along with him.
My advice is to limit cichlids to one species in a tank--thinking here of the South American species. Rift lake cichlids is another matter.