Hmm. Some aspects of this are reminiscent of the oldest of the GPSDOs I own.
The front panel says Z3804A Oscillator and Distribution Amplifier, and *IDN? says
HEWLETT-PACKARD,59551A,Prod. Eng.,3618-A
It also suffers from the 1024 week bug, and on the inside it looks like they grafted a GPS board onto a product that was previously just a nice OCXO and 10 port 10mhz distribution amplifier. Also I can't seem to get the holdover uncertainty below about 19-20 us. (My newer Samsung-rebranded Z3805A settles down to 800-900 ns) Nothing about it is as prototype as yours, but it feels like a smaller volume thing for a particular customer.
On the other hand, lots of 10mhz outputs and a line voltage supply, so I use it. Also IRIG-B output, which I bought a cute little Datum Timeview display for.