357, the great number of poles on the generator makes the output smoother than a 3 phase, I don't know how many poles are on an SA200, but my old Hobart has a bunch. Aditionally, the comutator is only conecting the peaks of the wave forms. While this would be to "noisy" for an audio circut, it is a darn smooth welding output.
With regard to the 3600 RPM 4 pole 3 phase Trailblazer You have calculated the ripple frequency properly. The output would be correctly refered to as 120 Hz 3 phase, as the frequency is counted based on a full cycle of one phase, just as line power is specified.
I would have liked to have one of those Trailblazers, but I ended up with a Ranger 9 instead.