GM-H supplied the stripes for dealer fitment. Certain colours were specified in ordering documentation. However as you say, in future judging of Sandmans i'd be letting any stripes go with any colour as they are not a factory fitted item.

As for radios, I'm pretty sure they were factory fitted when standard eg Statesman. Not 100% sure on who fitted the optional ones as there were so many variables. My HJ Premier has a dealer fitted Pioneer cassette player.