Does the horn have an underslung neck? (octave key on the bottom?) This vintage should have an underslung Microtuner neck. As for your question, The typical Naked lady engraving is seen on the professional horns (4M curved soprano, 6M alto, 10M tenor, 12M baritone and 14M bass) from 1934-1959. The Connqueror horns (26M alto and 30M tenor) also featured a similar engraving. A few of the older Conn artist horns had a portrait engraving, and there were a few other variations, transitional models, etc. Most likely it is a 6M.
As for the relacquer, sometimes it can be very hard to tell if the job is done right. My 10M was relaquered and the finish is so perfect it looks original. Sometimes the engraving will look a little worn. Also look around the tone holes and in the bell of the horn.
A professional quality relacquer will really pretty up an old jewell, and as far as lacquer effecting the sound, I think that if the relacquer is done right, the horn shouldn't sound any different than it did when it was new.