I have 7" GT and 4" FH together in a 7x4' tank and they are fine. They do get bored chasing each other in a big tank . Then again I have aro and stingray so they do distract them.
Yes it will work especially if you're starting from juvies, in that case you should put other juvies from recommended specieas above, black nasty, cuban, and other cichlids.