This should help with part numbers:

http://www.pbresource.com/sockets.html

What, no gray paint on the underside of the playfield?

Same here. Plus the gray paint gives it a "finished" look. The original Bally Kiss playfields were gray painted underneath. All the other pinball manufacturers had been doing it since the 1940's. In my opinion, without the gray paint, the playfields look cheap and unfinished. Like the manufacturer didn't care.

Here is something that should help.

Bally early ps pinout (resized).png