Sounds like a twin tube T8 fluorescent. I believe T5 fixtures (skinnier tubes) are 55w per tube. Like said, java fern, anubias, etc. would probably be great with your ~78watts total. A T5 fixture would be ~110w total.
FWIW, I've got a twin-tube 48" T5 on my 55. It's a cheapy Odyssea brand, $59 shipped, bulbs included. My water sprite and wisteria are taking over the tank, but like OC says, it's tough to get a good light/nutrient balance in a 55. I struggle a bit w/ algae.
FWIW, I just have a cheap gravel substrate and have had luck with my rooted plants rooting like mad. I'm sure the high dollar 'super plant duty' substrates are great, but I question if they're a necessity or not.