Same story, different ID. Same scenario has played out here hundreds of times over the years. OP asks for advice, and when advice goes against what their personal wants/desires are, they ultimately do what they want. What a surprise.
BTW - I have seen an adult GT that was properly cared for reach 11", at which time it was sold. Who knows, had that level of care continued it may have reached 12". Not sure what the norm is for this species, but an adult male GT is a large, deep bodied fish, and certainly will never reach it's full potential in a 55. I don't care what all the idjits in your TON of resources stated. Such as I assume yourself, most of those
resources have probably never kept a large cichlid such as a GT for its full life cycle, at least not what should be a
normal or typical full life cycle. There's a reason what one rarely sees clown loaches that are 12-14" TL (I have), or Oscars the size of
FINWIN
's, or Amphilophus in the 14-15" range, like the almost 12 year old Midas that I currently own.
Size of the glass box, is just the beginning of providing proper care for your pet fish.