Hi Amanico
First the dimensions and stern dial ofcourse !! But I browsed old catalogs look the same
Serial number
UNs archive works off the movement serial number. Their archive is not complete but you might be lucky if it is from their factory. Personally, at this time I cant see any evidence that it is.
Normally, UN's PW chronograph movements were signed ...
... and were finished to a high level. This does not really appear to be one, but I can be wrong, of course. Marcus