There are also various Tanganykian shell dwellers, Julidiochromis transcriptus, and Calvus that would work in a 40 (2 species, not all together.)
For Malawi cichlids there are a few species of mbuna or peacocks small enough to keep a group (1-2m/4-6f) given enough rocks/cover.
Severums grow way too large for a 40, a pair of firemouths would claim the whole tank as their territory.