A quick perusel of the tv history site (
http://www.tvhistory.tv/1950-1959.htm ) turned up a number of monochrome 27 inch sets in the 50s:
Admiral, Arvin, Capehart, Crosley, Emerson, Hallicrafters, Hoffman, Magnavox, Motorola, Muntz, Packard-bell, Philco, Setchell Carlson, and Zenith.
Oddly, no RCA, GE, Westinghouse, or Sylvania 27 inch monochrome models were found.
Many Dumont 30 inch sets were likely converted to 27 inch when the 30BP4 became unavailable.
jr