The rod style neck brace looks like a type that Conn stopped making around 1955.  The teardrop style chromatic F# key also looks like a feature of the Pan American, which was updated slightly and renamed the Director in 1955.  But the keywork is nickel plated and Conn introduced nickel plated keys in 1955.  So overall, it's kind of confusing.  It could be that Conn used some leftover Pan American parts to make a limited run of stencil horns around 1955.  BTW, I like the bell engraving.  Looks like a fun horn to own.  That thing can make a BIG sound.

One other thing.  It looks like it has a right hand G# trill key (right below the F key), which puts the body in the Pan American (pre-1955) vintage.  But then there are those pesky nickel keys.  Maybe nickel keys were introduced on the Pan Anerican before they were introduced on the Artist models.  Or maybe they were put on stencils before they were put on Conn-branded horns.  If we allow those possibilities, it could have been made any time between the change in the Pan American body style, in which the split bell keys were replaced with same side bell keys (estimated late 1940s), to 1955.