[GreenKeys] Help to identify an old "SELCAL" circuit board

[YIR]

I collect Teletype and related gear.  I have a circuit board with 32
chips
on it and after removing a couple of the large chips I discovered
a couple of Mars calls from 1974.  I suspect this board has to do with
"selective calling" in conjunction with using a Terminal Unit etc.
Hopefully someone will remember something about this board and
tell me what it is supposed to really do.  And of course where to find
technical data.

Please have a look at these photo links and let me know if you can help.

Thanks,  Pat  K7YIR   ex N0ETG  ex N0MOD  ex N0MTP

 http://mysite.verizon.net/res17bfm/selcal-1.jpg
 http://mysite.verizon.net/res17bfm/selcal-2.jpg
 http://mysite.verizon.net/res17bfm/selcal-3.jpg
 http://mysite.verizon.net/res17bfm/selcal-4.jpg
 http://mysite.verizon.net/res17bfm/selcal-5.jpg
 http://mysite.verizon.net/res17bfm/selcal-6.jpg