Other wear parts worth replacing
The short chrome outer shooter spring is 10-149 and rusts quickly. Fit a new 1-1/16" ball to protect the playfield, 3" leg levelers, a game-specific rubber ring kit, flipper rubbers and a shooter tip. A 3.58 MHz (3.579545) crystal is worth having, since a lead can break or the part can go missing.
Systems
Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part One, Clay Harrell (pinrepair.com)