best we start again from the beginning.
IC164 is responsible for signals 1-7, IC163 is responsible for signal 8.
It's a bit different on the driveboard, where PC4 is responsible for signals 1-4 and PC3 for signals 5-8.
Now please only measure the 8 signals, follow the path from the mainboard to the driveboard and enter the results again in a table. An example of the course of signal 1: Signal 1 goes to pin 1 (input) of IC164 on the gameboard and comes out again inverted from pin 16 (output). Then the signal 1 goes to the connector, via the wires to the driveboard connector, then the signal 1 goes on to pin 8 (input) of PC4 and comes out again on pin 9 (output).
For the signals 2-8 you will surely find out the signal course yourself.
First make a table with signal 1-8 at the input of IC164 and IC163,
then a table of signal 1-8 at the output of IC164 and IC163.
On the driveboard make a table of signal 1-8 at the input of PC4 and PC3,
then a table of signal 1-8 at the output of PC4 and PC3.
I hope you can understand my bad english, it's not so easy for me to explain complex troubleshooting in another language.