Good news on this.
I got the watch in the post yesterday and ripped into it.
The movement is toast but I've saved the TAG labeled coil cover.
The inside of the case / glass cleaned up well with my scratch brush.
The hands were stained etc. I might make them matt and I re lume them. I might just replace them as there are cheap enough ones out there.
The stem was broken but it came out of the crown ok.
The back of the dial was very rusty so I cleaned that off.
The very good news
the front of the dial cleaned up well with just my hanky and some spittle.
My photo is too dark but you'll probably get the idea.
I'm getting a very similar ETA 955 movement that will do the job.
I'm looking to have a very nice TAG Heuer in the next few weeks