My understanding of the radios in Australian delivered cars is as follows.
The 450 models came as standard with a Becker Mexico Cassette. This was a pinstripe unit until 1978, and then the one with the big knobs as outlined in the picture in the bottom right with auto reverse for 79 and 80. The pinstripe units are also not the same and changed every year or so. The 6.9 was as the 450. That picture is from a 1979 or 1980 owners manual. The Becker radios were not fitted by the factory, instead fitted in Australia from local stock.
The 350 didn't have a standard radio, but the dealer would fit a Becker if you ordered it and paid for it. Or you could fit something else.
The 280 was as the 350 until the update around 1975 or so. Then it got the Becker radio as standard, same as the 450. This corresponded to the huge price increase at the time. Its common for D-jet 280s to not have rear speakers even. I've also seen the AM only Europa dealer fitted to the early cars.