Hi welcome to the forum
What are their tank mates in the 75 at the moment? They are both big bruisers so any tank mate combos are going to be a challenge but it is possible. Maybe something like Auralis Barbs or Spanner Barbs would be a good choice? I like the idea of Rainbow Fish with Central Americans but not 100% with these two. Synodontis Catfish work well something like Eupterus or Angelicus would be big and robust enough to live with these, or some of the humbug catfish would too, the spotted are nice but not very active.
Bichir could work but I'd probably give these two as much of the bottom of the tank as possible. Same with adding other cichlids if these two have grown together it would be safer to not add any other cichlids. Severums are also better in softer water and centrals like yours are better in harder water.
Is the JD a regular or an Electric Blue? Carpintis is the better behaved of the Texas species so an other cichlid could work. Wondering about something like a Salvini or a Nicaraguan?
Wills