Aesthetically it's a very conservative looking guitar for a Mosrite. It's puts me in mind of the shape now used by the Washburn Idol series. It seems that Semie Moseley developed these guitars for the Japanese market. Here are his comments about the guitar:
"I was convinced I had to change my design, and I built this guitar called the Brass Rail. If I'd stuck with my original design and not spent so much money trying to come up with a new one, I could have made it. See, I put a 1/4" brass right into the neck 3/4" deep and I drove the frets right into it. Sustain like you never heard! I did necks both ways [bolt-on and set]. I mean, it was the ultimate in sustain. You could tune all the strings to zero and the first string would stay to pitch. So, I took a couple of these and let [a salesman] show them, and that's now I got into a deal in Japan."The example shown here is one of the set necks - the neck continues down inside the guitar underneath the pickups and right up to the bridge.
Apparently there were only about 100 of these built (as you can see in the photo, this is #74) but does that make this "the rarest of all Mosrites"? Well, for a production model, this is very likely true, but there were numerous custom one-off Mosrites including double- and triple-necks and these surely must be considered rarer. I'm also reminded of the trio of surfboard-inspired guitars that Semie built for Strawberry Alarm Clock.