So for the first round, starting at the inputs off SN74148 IC32 and 33:
2) Yes, both IC32 and 33 have pins 5 (EI) connected to GND.
3) With no buttons pressed, the EO output is in fact LOW. When any button is pressed, the associated EO pin does go HI.
4) With no buttons pressed, the GS output on both encoders is HIGH. When any button is pressed, the GS pins do go LOW.
5) With no buttons pressed, the A, B and C outputs of the two 74148 encoders are in fact high.
6) With above and no buttons pressed, all inputs to IC30 should be HIGH and all output LOW. This is what is happening EXCEPT for pin 9. With all other input pins, there is a clear +5V HIGH status. However, on pin 9, it is technically HIGH I guess, but only showing 1 volt rather than 5. I switched in another 7400, same thing.
7) Inputs to IC31 are all LOW
8) When I press any of the buttons, IC31 pin 10 does go to a HIGH logic state
9) When I press any of the number buttons, IC31 PIN 12 does remain LOW
10) When I press any of the FUNCTION buttons, IC31 pin 12 does go HIGH.
11) IC 31 pins 2, 14, and 4 are all LOW with no buttons pressed.
12) IF I press a number button, the binary value should appear on pins 2, 14 and 4. I think this is correct? When I press 1, Pin 2 goes HIGH, pins 14 and 4 are LOW. I missed it in my notes but I saw this change when I pressed 2 - I think 2 went LOW, 14 went HIGH and 4 went LOW, or maybe it was 4.. I'll have to recheck that but I seem to recall broadly these values were changing and seemed to align with binary although I wasn't sure how the pins correspond to a proper binary number.
13) If I press a FUNCTION button, I do get something like a binary value on IC31 pins 2, 14 and 4. If I press B, I get 111 going by the order of the pins you gave me. If I press a function key like L, the code is 101.
I should note - the keypad was in pieces when I received it - it uses foil tabs similar to those used on later Apple II+ keyboards. I put it back together by figuring out how the tabs oriented and where the little 'forks' that come down to make permanent connections to the matrix on the PCB match up to the points on the PCB. A couple of keys seem to be nonfunctional. There may be a reason why this was disassembled. And of course, it had to be missing one physical button.