Find the site
www.hnwhite.com. They have King literature from the H.N. White era of Kings.
The double brace (straight and C-shaped) is the 1910 Patent. I have two horns with that slide brace (High Pitch and Low Pitch) but they predate the curved bell brace. I believe one of mine (the Low Pitch) dates to 1915.
These are pretty small bore horns. The soldered on stockings often make for a somewhat sluggish slide. Friction fit means watch out if you are playing a lot of mutes. I've pushed mine apart at some really uncomfortable times.
Note that Sears also made a Silver Tone trombone, but it doesn't have the curved bell brace and the bell is not silver. There was a trademark suit from this and King lost. Thus was born the Silver Sonic.