Since a 40 breeder is your only option, this limits stock even more, and as far as cichlids go, I consider a 40 only large enough for dwarf cichlids, as adults.
As far as Central Americans, IMO the only one small enough is Amatitlania nanoluteus.
But ... you have plenty of South American, and African dwarfs, as well as 2 Indian species Etroplus maculates and canarensus, the later below .
40 breeder tanks are pretty good as grow out tanks, but very limited when it comes to adults, because there is no where for a less dominant individual to hide.
And remember the smaller the tank, the more frequent the water changes need to be to keep the fish from swimming in their own urine 24/7.