Unless someone can dig up some early '70s catalogs you may never know what it is. T-Mar may have a line on the year by the serial but I don't know how far back his data base goes.

Personally I would be skeptical of the one owner theory since I can't see anyone buying a brand new bike sans decals. Also since it seems to be missing handlebar tape (did he buy it like that also?) it likely needs a lot of work like overhauling the bearings, and cleaning everything. I think this may be a bit over priced unless all the work is done and it will give trouble free service all next yer.