Thanks, Jim -
Serial number is 5448461 - "Illinois Watch" so Hamilton, if I'm correct. I am FAR from an expert - Two watchmakers say the balance looks like it had a hammer taken to it, staff has been filed to a sharp point, has a very weak hairspring, and although not a big deal is missing two screws. It's so strange because the rest of the watch is excellent. Think maybe someone along the line pirated the balance for another watch. Category: caveat emptor.
The balance is usually serialized so it's not original if you change out the balance, but people do it, so it's just a matter of opinion.
That late of a serial number (1931) was finished by Hamilton and most likely has the 992E balance wheel with Elinvar HS in it.