@damon-mcqueary I don't know about the "5" prefix, but there's this:
https://www.trumpet-history.com/Early King Models.pdf
Here's a detail:
Also, there's no harm in contacting The H. N. White Company, LLC at https://www.hnwhite.com/ and Conn-Selmer http://www.selmer.com/en-us/instruments/band-instruments/trumpets/2055t .