Wow, I feel like I'm scrolling through the siren dreams thread! I never thought anything more would be found out about these sirens! The design is very similar to a Japanese Hankoku (I think) turbo siren, aside from the fact that those ones use the same motor for the blower and the chopper. The Japanese ones also use centrifugal blowers, direct drive off the bottom of the motor, and I assume they have pretty tight tolerances. The rusty one has quite a strange blower setup indeed... looks like maybe it has a blower bypass of some kind? There used to be a video of one on youtube, but it got removed.