If you are gonna go with a GT or JD, they have to be solo. Its barely enough space just for 1 when full grown. Anything above that like an RD or Midas is out of the question. If you wanna chance it, you are gonna end up with one fish in the end.
Either pick 1 cichlid thats appropriate for a 55 gallon, or go with the smaller 5-6 incher cichlids and dont overstock it.
If you want a GT or JD you can house other fish temporarily. But as the fish grows you will have to remove others or they will remove them for you also.