You would be better off keeping all 24 in the 55 to grow them out. Even juvies will be aggressive towards each other. Also, they will form a social pecking order as they grow, placing the 2 groups together later on can be tough.
In a 55, you can keep 15-18 adults. If you get a 75+, you could keep your whole group of 24. No need to cull males, as they will keep each other busy, giving the females time to relax.
You'll love the Maswa's, they are great fish.
hth
Justin