Probably not. Severums may be much larger then convicts, but they're much more docile , and once a pair of convicts form and breed the Sevs will either be torn up or forced into a corner where they must live in constant stress. Cories don't make the best cichlid tankmates, but given a secure hiding spot with a pair it can work, but absolutely not with two pairs of cichlids fighting over the tank.
The fact is Sevs grow to over 10" and a 55 gallon is full just with them. Alot of people underestimate the joy of giving a pair of cichlids a whole tank to do their thing - species tanks are highly underrated around here.