A close-up picture of the mouthpiece receiver of a 38B Connstellation. Note the letter "B", indicating it is has a trumpet leadpipe and not a cornet leadpipe, which would have been an "A". All models for which there is both a trumpet and a long cornet version (6A/6B and 10A/10B) starting in either 1958 or 1959 have this letter stamped on the mouthpiece receiver.
This picture also shows a close-up of the trigger assembly, and the two adjustment screws on the first slide stop. The setup on the 28A Connstellation long cornet is identical except it would have had an "A" on the leadpipe.
The 1955 through 1957 models for which there are both "A" and "B" models have the letter engraved on the leadpipe immediately following the name, as in the picture below.