Without having flown this particular aircraft:
According to Wikipedia, the aircraft is powered by the, non-turbocharged, Lycoming O-540-E4C5. This means that in a climb for instance, where you'd likely be at full throttle with this engine, if an engine stops (seizes), its indicated Manifold Pressure (MP) will be near ambient pressure, just like the other, running engines will be (at least for practical purposes), if it windmills, the engine will still work as a vacuum pump out of the throttle manifold, maintaining a still reasonable MP-setting. As the propeller will be windmilling initially, RPM is likely to, at least initially, stay in the same ballpark as the other engines (anyone who's flown older light piston aircraft will tell you most engine instruments are not accurate enough to make exact comparisons by value between the engines, try for instance syncing the propellers by the RPM gauge, and not by your ears). Unless the aircraft is equipped with torque indicators (not likely), the first instrument you will clearly be able to identify the engine failure is likely going to be the Exhaust Gas Temperature (EGT, an instrument I'm not sure if this aircraft is equipped with).
In a climb, or high powered cruise, the aerodynamic/kinesthetic feedback of the aircraft will be significant enough if you lose 1 of 3 engines, (deceleration, loss of climb performance, torque, change in sound) to warrant further investigation (and with proper training/experience, rather quickly conclude an engine failure). In a low powered descent, an engine failure can be quite insidious even on a light twin, and you are actually not likely to detect it until you apply power to level out.