While digging around in the archives on the NRC’s website I came across a rather odd picture on one of the documents (see below). The only context the article gave to the photo was: Seabrook siren trucks. The siren is composed of what looks to be two WPS-4008 heads attached upside down to a single rotator. I highly suspect that these are what Whelen advertised as the WPS-4000-II, though I could be wrong. A quick google search for “Seabrook siren truck” brought up a few articles from ‘88 and ‘89 discussing Seabrook’s plan to use truck mounted sirens in the event of an emergency. I wasn’t able to find any posts talking about these strange units, so forgive me if this is already common knowledge.
Photo Source: US NRC: Fundementals for Emergency Preparedness (Page 147) (https://www.nrc.gov/docs/ML1111/ML111110898.pdf)