Identifying mystery TI ICs (Motorola MDP-1000 investigation continues...)

[Josh Dersch]

More mysteries while poking at the MDP-1000.  Spent some time this evening
working out the rest of the signals on the power harness (I suspect inputs
for an LTC circuit and a "power good" signal, as well as something
connected to a relay on the backplane, probably related to power control).

There are a lot of unidentifiable ICs on the main CPU logic board and on
the backplane, mixed in with bog-standard 7400-series TTL.  Curious if
anyone has any ideas, as my searches and perusal of datasheets/databooks on
Bitsavers have turned up nothing.  These are all TI-manufactured ICs, 1969
manufacturing dates, with "SN48xx" and "SN63xx" part numbers (a few omit
the "SN" prefix.)  I'm wondering if these are just standard 7400 ICs with
special codes; for example there are several SN4816's near the edge
connector for the I/O bus, where a 7416 might (?) make sense, and from some
basic probing and following traces I think the pinouts make sense.
(Everything's conformal coated so it's a real bear to beep things out...)

Any ideas?

Thanks again,
Josh