you might need a bit more width and depth, could you stretch to 72x30x30 as that would be better or red fin giant gouramis dont get quite as big and could go in a 180
I would of said a 180 is big enough for one but their growth is unpredictable i know someone who has a 16 incher in a 8ft tank and its been that big for years but my local aquarium has a 26 incher in a similar sized tank.