As mentioned by w e, at the time yours were made, they would have been on a sticker on the back of the tweeter baffle like you can see here:?
/g/DahlquistSpeakers/wikiimage/10202?As the baffles are missing altogether on yours, the serials would've gone with them.
Good luck with saving them. The more work you put into restoring a set of speakers, the more you'll appreciate them in the end. It's a great feeling bringing a dead set back to life.
