My guess is that you have a short somewhere and that all of your old boards in fact are probably ok.

This happened when you were changing bulbs.....before you did that everything worked 100%..correct?
Did you lift the playfield when you changed the bulbs? Did the problems start after you lifted the playfield?

I am guessing that you have a something shorted...... a switch to a coil or a lamp to a switch.

Look for pinched wires, loose wires and anything out of place underneath.

You have all brand new boards, your problem HAS to be wiring or some hidden fuse block..maybe a wire came loose from the power supply under the table. Something like that.

When you do discover the problem, I will buy your old Gottlieb mpu and driver board if you want to sale them.

Good luck.

Ni-Wumpf manual. http://www.ni-wumpf.com/Gottlieb/System%201/System1Manual.pdf

Specifically....read the trouble-shooting part about if led remain lit.

I would go a step further..........

1) Unplug the machine from power
2) Unplug all the wires going to the DRIVER board from the body of the pinball machine.
Leave the driver board plugged into the mpu board.
3) Plug machine in and power up and watch the led on the mpu.... same or working?

If it works now with all driver board wires disconnected you have a short someplace.
If it's the same as before, you do not have a short and your mpu is suspect.

EDIT... ASSUMING you have checked all your wire harnesses and they are all good as others have suggested above.

Yep I agree.... ESPECIALLY that big ass connector that goes from the mpu to the driver board.