TubeNet

1) Like everything else, probably started in the 1920's and ended at the onset of WWII;
2) Like everything else, probably would have to source used parts or reengineer for current available parts.

Here are the folks that will know for sure, if there is any for sure to be known:
hnwhite.com

I played an overhauled/refurbished King Giant sousa back in HS. It had the standard (old style) neck and bits you'd find on other King sousas. The "old style" (tall) neck or "new style" (short) neck should both fit. Great sousaphone -- similar in size to a Yamaha 411 or Conn 20K. Wish they were still made