Re: conn made martin?
That serial # would put in the mid to late 1930s as a Martin. That would be the era of the Committee and the Standard. Does it resemble any of these pics of a Committee or Standard? http://saxpics.com/?v=gal&c=1611
Never heard of a Martin made by Conn, although there were some stencils (not Conn or Martin branded) that had features common to more than one manufacturer.
If it has soldered rings for toneholes, as opposed to toneholes drawn out of the body, it most likely came from the Martin factory unless it is a truly ancient horn.