The Nova fixture would give you high light, not the low light needed to do without CO2. The Coralife fixture, if it has reflectors as good as AH Supply will also give you too much light to do without CO2. But, I don't think it does have AHS quality reflectors.
A 55 gallon tank is only about 12 inches from front glass to back glass, so a light fixture with the bulbs in a line will work fine on it. I suggest you go with the Coralife fixture, but look for a way to raise it a bit if necessary, and it probably will be necessary.