I've only been able to keep them in a species-only tank. Had several generations in a 40B...
Several? Do deformities occur throughout the generations as often compared to other cichlids like Convicts?
None at all.
If you're seeing deformities in a generation or two of inbreeding in any kind of fish, either there are problems with the original stock or the deformities are arising from issues with raising the fry.
Just look at fish like Red Tiger Motaguense - all of the fish in the hobby are descended from a handful of pairs in 2006 or so.