Visual Pinball! Cool! I know that side controllers for the flippers are relatively common, but I have never seen a cabinet with real plungers!!! That would be very impressive. How do you configure that input to feed into MAME?

Well actually it's VPinMAME that would be used for Visual Pinball controls. MAME itself doesn't have any Visual Pinball support to my knowledge.

Here's a good look at a prett neat plunger install:



Taken from this cabinet page.

Simple design, just a microswitch that's normally closed, and opens when you pull back the plunger.