The Century is actually the equivalent of the GA-20T, known as the Ranger or Crest, depending on the exact year. I've owned a '57 GA-20T and '58 GA-20T - both two tone era Gibson combos - and they are 100% identical to the Epiphone Century. Great amps! Similar to a tweed Tremolux, but not as big sounding.
I would love to speak with someone at Gibson about these, but I have no idea where to start.
Here are some daylight photos of them. I currently own five 1959 Epiphone amplifiers so far...