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

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