Hi I don't know if you will get this, but I never liked the rear end of my SM so having looked at a few tail tidy mods, made my own and it worked out better than I expected. I can't upload the picture on this comment box as I would like to share it.
Thanks for the tip, I’ve followed your example and very pleased with the result. The only thing I did differently is that I removed the old plate mount completely - just 3 x 10mm nuts - and mounted the new plate directly on the fender with tape. As you say, each to etc. cheers.