An adult common BCI or Dum is not going to fit well in a 55 gallon tank as it's too narrow. One of my adult BRB's came with one, and he did fit in it, but he's a slender boa. A dwarf dum that tops out at 5', an adult male BRB, or one of the smaller locality BCI's like a Sonoran or Tarahumara would also fit.
The problem with all of these is screen top = problems maintaining humidity. There are threads where people have shown how they altered their 55-gal tanks to be used on their sides, with plexiglass drop-doors installed on the top (which is now the side), to give the snake more floor space and improve heat and humidity retention. Here is a recent one: http://ball-pythons.net/forums/showt...a-tank-on-side