It won't fit unless it's a custom built stand. Even a 40 would be tough but will probably work with a 120. My 75 has a 40b as a sump and I had to make the stand wider since both tanks are 18 inches wide. I think a 55 is to high to work with but that's completely up to you as long as you plan for it the 55 will work. It will be to high getting a skimmer in will be very hard. So it really comes down to building a stand to fit whatever you decide.
Well mine is a FOWLR so the slimmer part isn't anything to be worried about. Like I said I'll measure when I get home an post back. Thanks for the input