I¹ve seen some ads on Ebay for an Al Cass mouthpiece with a trombone rim and a small cup and a trumpet shank. This makes doubling on trumpet easy(?) for trombonists. It would seem to me that in order to play a trumpet high C (Bb concert) you¹d have to buzz a double high trombone Bb. Am I right on this one? Thanks, Dean Hubbard