Rear shelf 6x9 Question

Our 74 Gold Duster has these cutouts, I have some pictures if that helps your question on my Members Restoration page. I dont know about the code for the option, this weeks project is finally fully decoding my VIN and Fender Tag for Duster & Valiant. Just found build sheet on Duster, under rear seat, which I was pretty excited to find even existed 40 years later.