Dunbar-Nunn 480k production period?

[Lundy]

Would a D-N Unitrol 480k be period correct for 1982? Even better, if anybody has information on the production period of the 480k siren? LAPD has used them since at least the mid 80s, but when did they officially switch from the FS PA-20?

 

[Windycity411]

Not sure about that model, but I do recall that brand in Illinois in the 80’s. Not sure if it was in a St Regis, Fox body LTD or a Diplomat. I definitely remember a slide switch with YRB indicator lights.