Internal balanced..what damper do I need

I do believe the 'BI' at the end of the part number means 'Balanced, Internal'......

So is this the same car with the Mutha Thumpr cam? With a rough cam like that, I would expect the AFR to bounce around, so you will only get a general or average idea of AFR. The mixture can be bouncing around quite a bit from cylinder to cylinder, so I would not take the AFR info as being accurate for all cylinders.

With that cam, it is no surprise to be rough at idle....