The gun sight of P_51B/C and Mustang III

Hi !!!
It is my first time, I need your help . I've been building the Mustang III model.Its cockpit is about to be finished.Unfortunatelly, it had to be scratch-built.I found out, the Mustangs III were equipted with the Spitfire gunsight. I haven't found any picture or drawing yet ,what the one looks like. .Could you help me.

P.S Sorry for my mistakes, I'm still studding english languege.

This may help. Its the cockpit of a Mustang C that I took at Duxford earlier in the year. I suggest you be cautious as I cannot promise that the sight hasn't been changed over the years, but its better than nothing.
Also note that the ring sight folds up and I think was used as a backup should the reflector sight have a malfunction.

Hope this helps

David