1965 Dodge Dart 270 wagon

Today I vent to the State inspection and I got one thing to take care of. The idler arm was shoot!! So I will do the change tomorrow.

I did some serious cleaning today and found one marking on the fire wall, one script on the right inner fender "1520" . I don't know what any of them means. Any help is appriciated.

Since this is an A/C wagon I found on the right rear quarter window an Airtemp sticker. Never ever seen one on a 65 Dart. Any one else?