The M body is Martin's Grand Auditorium (0000) shape — similar to a 000 from the front, but at 16 inches it's Martin's widest body. The depth is close to a 000, so it's comfortable to play, while the wider body gives it a balanced, powerful sound. The back is 3-piece construction, like the Style 35.
Excellent condition. The tuners were changed to Waverlys by a previous owner — I don't have the originals. I recently had it set up through Wood Street Guitars in Oakland, and they gave it a clean bill of health. Comes with the original Martin hardshell case.
I picked this up in a trade a couple of years ago. It's a genuinely nice guitar and I enjoy playing it, but I mostly reach for my electric, so this one's been sitting unplayed more than it deserves. I don't have any history on it before I got it.
Not interested in trades! Unless you you have Suhr S Classic!