I had a 24B6300 Philco a few years ago. It was a 1954 model 24" set with doors. I had found an ad for it that mentioned that Philco had sets with up to 27" tubes but never could find a reference to any 27Bxxxx sets anywhere. This is the first time I have seen one of the 27" sets. There is a copy of the dealer brochure showing both the 6300 and 7300 sets at the TV History website:
http://www.tvhistory.tv/1954-Philco-Brochure2.jpg
I had restored the 24" set and it was a great performer. It had the built-in UHF tuner that I am guessing was installed by the dealer. The model on the set was 24B6300 with a U added at the end in pencil. All of the references to the UHF sets had the U after the B in the model number (i.e. 24BU6300).