Before you get too excited, that's a reproduction bike, made in china, late 90's, early 2000.
You can tell by the parts. Reflectors, etc.
It's really not much of a reproduction, either, as mercury was a murray brand (murray actually made great bikes up to the 50's, along with huffy, which used to be huffman) and would of been a straight bar before 1950, and a middleweight cantelever schwinn-type frame in the 50's, but without the oversized tubing like the one you posted.
It's definitely a repro. I would have to fabricate for a front brake. Possibly a disc. Price was $75. If I decide not to use it on the build, I think I could always get my investment back. I just think it would be a cool looking MB.