The reason to do the test as I suggested is because it doesn't require you to measure the torque on the coil by the magnets. The torque is constant, by gravity. measuring rpm is easy, measuring torque isn't, especially if the torque is fluctuating due to the torque not being constant, because the rectifier either doesn't draw constant power, or its a single phase test coil.
you can do the tests with a single test coil, and the results will correlate well to 3 test coils connected in delta. but they won't when connected in Y. the reason being the third harmonic is canceled out and "missing".
so for example on my 3 phase generator, the phase to neutral voltage was 138 or maybe 142, but the phase to phase was 230. 10-16 volts went missing. however, it did produce a very nice sine wave.
basically all you need is a test coil, a scale to weigh it, then wind up the string around the generator shaft, short the coil, and measure the peak rpm of the rotor. then compare with thinner coils and closer magnet spacing, or wider coils, etc.. or coils with bigger or smaller ID or also the OD.