Compass Mk III messed up

Here is my rather messed up Mk III compass that I am hoping to restore as the people I sent it to originally here in W.A ended up smashing the glass in the slipper ring, lost screws, broke the prism and then handed it back to me with a note saying sorry they cannot fix it!!!! Gads what a pack of wallas :red face:
So now I am going to try and do it carefully myself have read articles posted by Mr Laidler and feel pretty sure I can do the job.....well at least better than the other people.
It is a TG & Co Ltd London 1943

Well, we just saw one done, I'm sure he'll give you all the info you need...and then there's Peter...

That is a VERY early Mk3. Only ever seen 1 before. They were changed early in production to move the filler plug from the top to the side to ease/speed-up production. The orientation glass (case top) cover guard was a later modification and it didn't matter whether they were cheese or round head screws, just so long as they were brass of course