I always used Manometers to balance Carb and EFI systems. You can do this using vacuum tranducers and dual tracing, however, the cost and time using a scope to do this doesn't seem practical. It sounds really neat what your wanting to do, but what price are you willing to pay? There is a very wide spectrum of transducers to use. A homemade one out of a GM Manifold Absolute Pressure Sensor is cheap to build. This will get you there. You can also go on the high end with a piezo-sensitive one or two should I say. You might be able to get two of these for $1200 US dollars. The afore mentioned will actually launch you into engine pulses more so than actual absolute vacuum. The waveform will translate into high and low peaks.
A manometer is steady. Just something to think about.