I have A121 and it has a matching 303 mag. Seems I picked this up maybe two years ago on Gunbroker. I believe I paid around $1500 for it but my memory isn't the best. It may have been closer to $1800. Don't know if that helps on value for the subject rifle of this thread.
Below are a couple of fuzzy pictures of mine.
Mine didn't have the sight disk holder:
Hope this information helps,
Brian B