I don't know how active this thread is as of right now, but as a Rockfordian myself, I got some information about the sirens.
As far as everyone knows, Rockford consisted of 3 Chrysler Bell Sirens. 1 Atop of said Talcott building, one on top of the Rockford Ordnance/Essex Wire plant (Now Demolished) and one on top of the East Highschool building.
I have heard on and off reports of them running the sirens through the early to mid 60s, some reports saying they stopped testing at 1960 sharp. All of the Sirens were supposedly removed in the 80s, after an estimated 2 decades of silence. I'd like to say late 80s on most of the removals, but my dates aren't completely accurate.
From that point on, the city was sirenless with the exception of the Volunteer Fire stations, which mostly used Federal Signal models (Although I have seen some ACA models, to which I do not remember model names). It was in 2003 when they added the new T-128's. They had installed them after a large, but not tornadic, storm blew through, knocking out power through a large portion of the town. Those still stand at multiple areas today.
With this post, I attached an image of the Ordnance Plant siren, this one was reportedly removed in 1984, but again, my dates are iffy.
But as I know, there were no such ACA Alertors around Rockford whatsoever. I believe there was a Hurricane, and maybe a few others, but no Alertors come to memory within my circles. Belvedere I know had Thunderbolts up until last year, and I remember plenty of Alertors closer in towards Chicago, but none here. Hope I helped!