In my experience, some of the key points to note for pinning down the year/brand/model are:
Type of drive (Transverse(TS), Vibrating Shuttle(VS), etc)
Type and location of tension
Slide type
Type, shape and location of bobbin winder
Importers badge or badge style
Finial style on top of needlebar and presser foot
Casting differences in bed
Rear access panel shape
Serial number