It was a random number on the board, I used to have a dozen random boards like this some populated with lots of silver cans, they came with a bunch of AT style motherboard scrap
this one managed to miss my last recycling run as I never knew what purpose these served.
I've been doing a lot of IBM documentation scanning from that era because so little was generally known about their products in the hobby community.
Now there's a small but growing community of people hacking on 80s IBM comms and midrange equipment.
I don't think its out of a 3174. I own a couple and there is is nothing like that in any of them. However similar boards are found in lots of other IBM equipment from tape drives, disk drives down to the Selectric Electronic Composer...
The stopper for a lot of people is IBM-unique labeling and parts. I can clearly see Intel, Hitachi, Mitsubishi, Motorola and TI logos on the ICs on that board, but they're all house-numbered. And what do you do about the IBM silver-can hybrid circuits?
You can make some guesses--the Intel 40 pin DIP might be an 8085 with SRAM off to the right of it. But that would only be a guess--it could also be an 8051 or some custom design.