I don't have a problem with the Hampden any more, as you can see in my shot of the aircraft in post #10.
The shots in post #2 are very old screenies from when I first tried it out in FSX, and the transparent prop discs were the result of a flawed download ( the flaw was in the files, not in the download process itself ). Mal998 at first provided me with the three prop textures as above, but that didn't resolve the issue. Eventually he provided a correct version of the download and everything was fine.
So now I have two Hampden downloads - the faulty one and the corrected one. Out of curiosity I deliberately installed the faulty one this afternoon into P3Dv2.4, and strangely enough it was all okay. So it seems the transparent prop discs as shown in post #2, and which...