Many thanks!
http://www.nostalgiaair.org/PagesByModel/421/M0001421.pdf
It basically comes down to examining the volume control of your set and determining which of the three different implementations it has. The Riders writeup explains this fairly clearly.
I believe that Pooley and Red Lion were the chief wooden-cabinet makers for AK. There were probably others. AK made their metal cabinets in-house.