I have Synodontis eupterus in with my JD trio and adult turquoise severums.
I also have a second eupterus in a 55 with 6 adult robertsoni.
Both get along great with their tankmates.
These are really neat Synos and get to around 6-8" and are a full bodied Syno. Nice high dorsal fin. Very comical in the nature as well.
This would be my choice