You can take those legs off and set the fixture right onto a dual bulb Versa-top. I think the legs are junk, if you're like me you won't want to use them anyway, they also allow for a bunch of scattered light into the room. Waste of time, energy and plastic, IMO, nice dust catchers. I think the non-adjustable type Coralife legs will fit that Catalina (and the Coralife, obviously), they still allow for light spillage but are a lot more practical than those stupid lip-mount adjustables.
I love open tops, but I've also lost a lot of fish to it.