There are several 'types' of Indiana horns made by Martin. Several different grades of horns under the same generic Indiana name. I am not an expert, but I own one of the good Indiana horns, and it definantly has a better tone than a Bundy II. I don't play, I am a restorer, so I can't comment on the playability, but my son has used both and says it's a matter of comfort. The Martin requires a little more strength I've been told.
Mid-50s horn should be a good one, or it could have some of the features below and not others.
Things to look for on an Indiana:
Nickel keywork.
Adjustable right thumbrest.
Bird cage, not sheetmetal lower tonehole guards.
More engraving, not block letters, 'Indiana' slanted, with a fleur below the name, and an Indian head in profile above the name engraving.
Some of these are on the Alto and not the Tenor, and vice-versa.