Quoted from Geee:Are the schematics the same for all machines with the same MPU? So are the circuit boards, etc interchangeable?
Generally the schematics for the MPU will be the same, but the other components are often different.
Example: Pinwiki had a chart for the Williams system 6 games and shows different sound boards.
http://www.pinwiki.com/wiki/index.php?title=Williams_System_3_-_7#System_6
What game?
Also, welcome to Pinside!