Does anyone know anything about a mouthpiece marked as Ambassador 5?

I purchased Mason's Olds Special and got it in the mail today. To test out the horn, I pulled out a trusty Olds 3 mp and tooted away on the horn. Then I noticed that inside the case was a mouthpiece, an Ambassador 5.

The shank is small shank trombone. But the mouthpiece cup is tiny! I'm tempted to try this on my alto to see how it sounds.

--Andy in OKC