Its hard to tell from the photo provided. Do you have any detail pictures of the rear dropouts, BB and seat tube/seat stay area? Might help narrow down the list of possiblities a bit. Oh, and I would check the BB threading before you cut anything off (personally, I'd leave everything on anyways). Those gold brakes make me think Mafac, which makes me think French, which makes me think French Threaded. And French threaded isn't going to make a fixed conversion very easy.