Wait, isn't a standard 55 18in tall? I believe it is. You would have plenty of room under there for the 55. Servicing it might be tight, but no tighter than doing 2 30 gal. The only trick is getting it into the stand. No you wont have to drain it. Just temporarily take out one of the braces between the doors. Slide the 55 in and replace the brace. No problem. Likewise if you want to cut a hole in the side of the stand then slide it in that way. But then you have to repair the hole. The other way is a piece of cake really.