I guess I will add the game has another issue that probably points toward the board:
The audit menu behaves bizarrely.
When the self test button on the coin door is hit, the machine enters audit mode. A and B cycle functions appropriately. "Enter" works to enter into self test submenu, but will not work to enter an individual test, which cannot be started. Most numeric buttons on the keypad cause the machine to put out a bomb sound in any part of the audit menu, and the audit menu is reinitialized (!). When cycling through the self test submenu, a numeric key, when hit, appears on the display. A second numeric press will cause the bomb sound and restart the audit menu (inputting the values for the tests did not work).
The clear button works as expected, the "game" button does not.
The board still has its original battery, which hasn't leaked but could be causing memory problems. I'll be replacing it shortly (likely this weekend).
I tried disconnecting the audit remote, but it has no effect on the switch matrix issue.
Went ahead and swapped out old battery for a battery pack with a blocking diode and reseated each PIA and swapped their positions.
Still boots, but it lost its free play setting, the audit menu is still screwed up, and I discovered the coin door is isn't working. High score initials (only) are junk characters now. Needs reset from audit menu, which isn't working.
Keypad is wrapped in tape. I'll have to dismantle it and see whether there is a problem there, but now I can't even test the dead switch row.
Will look to the coin door for issues.