So. America Cichlids Suggestions

Group,

I have a 55 gal well established tank the needs repopulating. I have had
angels for many years and they are starting to go (old age I think). I have
standard gravel with a undergravel filter and the pH is consistently between
6.3 and 6.5. Rather than get more angles I was thinking of going with fish
with more of a personality. Non-angel and non-discus Cichlids came to
mind. I don't want to turn the tank upside down by changing the gravel for
crushed coral to get the hard water so African cichlids are out.

Here is my question: What types of So American cichlids would work under
those conditions. Ideally I would like to have 3 varieties that can coexist
given enough structure. I plan on getting them young, how many of each
should I get? Would I need to cull them out for a pair of each type or
would 3 or 4 of a type work?

I think I know just enough to be dangerous so I am looking for experience.

Thanks,
Steve