You would need the trigger on C for sync so you can identify the cylinder events on A and B.
Whatever cylinder is in the bank A position one will be trigger out. So, just select the same polarity secondary probe for channel C trigger as bank A.
As long as you split the cylinders by polarity between the mixer bank A and B, the order of them does not matter. The events will be displayed in the firing order.
Hope this is helpful.
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