In the invaluable tome titled "The Union Pacific Streamliners" the first chapter of the book is dedicated to the M-10000 and its descendants. On page 40 the only mention of the horns used on the first train set declares that they were Tyfon horns (no mention of the specific model). They were designed to be audible at one-half mile in still air and to sound as much like a steam whistle as possible. They were also chrome plated (mentioned elsewhere in a photo caption).
Tyfon might have been a separate business way back when. I have heard the words "Leslie-Tyfon" used together as a horn type, but seemingly not valid for that era.
Edit: Tyfon was originally a ship horn. Leslie was involved with Tyfon horns in the early 1930's
