The 16 ga. graded guns (as in A,B,C) were all in the 200,000 S/N series; the Sterlingworth 16s in the 300,000 so it appears you do have a Sterlingworth. According to the year of production info this site, it would date to 1934--a Savage-produced Fox. I think it's probably the same snap-on iron either way. I've got a Philly SW 16. I'll pop the iron out of the forend tomorrow and take some pictures if outdoor light is good. In the meantime someone may come along who's already got a foto.
It's entirely possible that Bobby Brook (bbman3) might have an iron for a 16 or know where you can get one without fabricating it. Sometimes Foxes are parted out on eBay or GunBroker so another possibility there. Nice surprise for you dad!
jack
