I haven't yet wrapped up all the loose ends of this project, but I know there are a couple of you who have been waiting for this for a while now, so I wanted to show you that I haven't forgotten about this!
As you can see below, I haven't yet found a suitable glass stone for the center of the medallion, and I still need to track down some suitable hardware for the chain and clasp. But here it is as is looks today...
And here's a screen cap of the original
It measures 100 mms from top to bottom, and about 64mms wide and it's pretty heavy. Thanks to Alancastillo for the measurements of the costume rubber meddallion.
I'll update when I've sourced the finishing pieces.
EDIT: See post 6 below for a newer, crisper casting.