Are there any markings inside the case that would indicate a manufacturer?
The 15 jewel movement is not particularly high grade, nor well finished, but then again, Ulysse Nardin went through a relatively low point during the post WW2 years.
My feeling is that this watch may be an older UN movement (although it appears remarkably similar to a Marc Favre movement) that has later been re-cased and had a dial made in a much earlier style. Unless there are case markings that indicate otherwise, that would be my most optimistic assessment. Other than that, I would be inclined to think that the whole watch may be a fantasy piece.