Hello,
I've been following this thread and just have to ask...
I saw on one of the datasheets above that the timing accuracy is at least 150ns plus a few millis once you add the other network overheads. There's been a lot of progress on GPS chipsets in the last 20(!) years, have you considered using a modern timing unit like ublox M8T and say a raspberry pi or similar?
Don't get me wrong, i know and love fixing old gear, but i also consider the performance of the fixed unit and the usefulness of the knowledge i gain repairing it, and to me this units seem like a bad proposition?