IC1 is a 75140 dual line receiver, where pin 6 is a reference and pin 2 is a strobe, so pretty much what you thought.

Also of interest is IC101, a 75122 triple line receiver, which has a Schmitt trigger, two AND gates and a NOR for each line. Most of the pins are tied to ground (1, 2, 3, 4, 12) so it's used as a buffer, ignoring the rest of the logic.

For IC3A-D, I think what's going on with the symbols is a briefly-popular way of representing positive logic and negative logic by changing the symbols so a wire has bubbles on both ends. In other words, if you have active-high inputs, represent it as a NAND gate, but if you have active low inputs, represent it as an OR gate with inverters on the inputs. It's the same gate, just drawn to indicate if it's performing an AND or OR. Note the way the bubbles move on the inverters too.