I'm not trying to make this one look good.. Just curious if its safe to shoot..
That pitting on the receiver looks pretty deep and shiny bores can be deceptive ( makes me wonder what they were trying to hide)
I will err on the extreme side of caution because of the injury potential and recommend you call an NDT firm close to you and see if they will X ray or UT it. ( should cost around $100 for a drive by item and they might cut you some slack in the south)
The only other option is a proof load but that runs the risk of destroying the weapon and often a shock load can "create" cracks that were not previously there thus giving a false sense of security.
You would need to break the barrel from the receiver and test both
If you wanted to repair those pits on the receiver- you could TIG them then dress/finish and it would blue beautifully ( but that's work and would exceed the value of the weapon unless you had access to the stuff and wanted a project)
Personally, I would re barrel to a different caliber for that part but that's just me.