Quoted from DumbAss:

That plunger and link is for the "WPC style extension return spring". Williams part number for the spring is 10-364.
The tapered plunger and link (currently installed in this machine) is for the "System 11 style compression return spring". Williams part number for the spring is 10-376.

Williams used the stop A-12111 (typically brass in color) up to Twilight Zone (last pre-DCS machine). Starting with Indiana Jones (DCS machine) the stop was switched to A-12390 (typically black in color).
The White Water upper right flipper actually uses a System 11 style flipper. The reason is due to the limited space at the point of attachment of the return spring to the crank assembly. When I shopped out my White Water I changed the System 11 style flipper to a WPC style flipper and it kept getting caught up in the tight space. That's why Williams chose to use the System 11 style flipper here. The manual actually specifies this. It's just buried in part numbers.
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