Are the switches original/untouched? Or did you remove or replace the switches during the swap?

Try a jumper across just the wires (Bypassing the switch and the diode) to see if they respond.

So, they work (Appear correctly) when you jumper across the solder lugs at each switch? But don't when you manually close the target?

If that is what is happening, it sounds like the diodes are shot. You can jumper across just the diode and verify that the switch responds (make sure no drop targets are down or can get ghost switches appearing). If the switches work when the diode is jumpered, the diodes are either bad, or installed in the wrong direction.

Well, there is a 0.7 voltage drop through a 1N4148 diode. Did it work when you jumpered past only the diode?

With that slight voltage drop, it is possible that a weak output from the PIA (Through the connector) could result in a return signal being too weak to trigger the input to the PIA. If it has IDC connectors (The kind where the wire is simply stamped down into the V of the pins) one might be pulling up. Otherwise, it could be a bad PIA. You might want to swap U10 and U11 and see if the symptom changes.

Are there any other switches that work which are on that same row or column as the 4 that don't work?

No. It doesn't make sense that the switches function and appear when you bypass each diode. That makes it sound like it is:

1. The switch matrix interface chips on the MPU (you say its a working Altek)
2. A weak connection from the Connector on the MPU to the Playfield.
3. An almost broken wire on the playfield (like there is just 1 strand of wire left connected).
4. The diodes are in backwards or the strobe and return wires are reversed at each switch (were working prior).

Sorry, but I am out of ideas. I would be looking at the signals with a scope. Both at the switches themselves, as well as the strobe outputs and switch returns (with a switch closed) at the MPU board ICs.