I would try Eurobracing the tank if you wanted to remove the centre brace.
Get some 2"-3" wide, 3/8" - 1/2" thick glass strips cut to size from a local glass shop and silicone them in to place, should be good to go (As Danny said, the tank would have to be empty). My 62g is eurobraced and I like the centre being completely open. Easier to move around and fiddle in the tank when you need to, as well as the lighting thing.
My only concern might be that 1/4" glass seems a little thin for a 56g tank. Esp. at 48" long.
. Maybe I just feel safer with overkill!
My 62g is 3/8" with 1/2" eurobracing and is 40"l x 18"w x 20"h.