In some cases it might be easier to detect certain game situations by also reading inserts and/or switches instead of 'just' flashers and coils. Inserts can definitely be read with the Pinduino - for switches you'd need an extension like the SwitchShield.
In your example you could simply monitor the bell opto and you're done.
But you need the above mentioned extension and more cables and connectors of course....

But you´ve assembled it very nicely
Bummer that it interferes with your connectors on the board! Can I do something about the layout of the SwitchShield? Although I´d hate to throw away the 50 boards I have here.....

you´re right, I looked at the layout of the Pinduino again and I couldn´t possibly change the SwitchShield in a way that would free up your J6/J7 headers.

I was lucky when I designed my PinLightShield stackable from the very beginning without even having the SwitchShield in mind by then. When the request for switch detection came up from some users it was easy to put that on top of the PinLightShield.

I never published my board design because I always wanted to do an improved version which I never got around to.....
But my library is open sourced and you can find the link in the thread Eric mentioned.
And in fact all you need is the software, because my hardware works exactly on the same principle as Eric´s and you definitely can monitor inserts with that hardware. You just need a bit more software to monitor inserts due to the way WPC and other systems control them.
My library takes care of that handling.

I have included the above mentioned circuitry on my PinLightShield (https://pinside.com/pinball/forum/topic/always-wanted-to-build-your-own-pinball-lightmod) and can confirm that it works just fine for detecting GI - at least in older games that use 6.3VAC for the GI. I don´t know what voltage they use in the newer games and whether it´s AC or DC.