I have gathered miscellanous comments, news etc. concerning Dylan and the harmonica, mainly from r.m.d. SOme one mentioned that Bob played Marine Band. On the other hand MBs are slightly more powerful in tone quality. SO if you aren't sure about it, it could be that he is playing Blues harps. But I have no real info regarding Bob, I just always thought that blues harps were tuned to a different scale.
Scale is the same.
As noted above, the Blues Harp does not have the powerful, clear sound of the Marine Band, so it has never been as popular with professional musicians. Bob Dylan, as far as i know, started out with the Marine Band and always has used that brand. I found this posted by Patricia Jungwirth on rec.music.dylan. She gave me permission to cross post. However since the arrangement of notes is the same for all ten-hole diatonic harmonicas, you may use a harmonica in a key other than that indicated in the legend of a specific song.