About what instruments to have in a test bed, an indispensable one is a good blow by meter.
It does not have to be sophisticated. It can be just an orifice meter, preferably calibrated against a std source.
BBY is the only test variable that will warn you of an impending disaster before it happens!

I have been flying with one I developed for the last 10 years or so with full disclosure to FAA (Form 337).
Miguel Azevedo

Not too useful in a rotary. What you are mainly concerned with is apex seal leakage.
The apex seal leaks  from one chamber to the next. Not to the "crankcase". A piston engine
is fundamentally different. Any leaking piston  ring leaks to the crankcase.

Paul Lamar

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