From the photograph rust removal should come a little further down the list of things to be doing. The gun is obvious of the face by the gap at the barrel to breach top either by not locking up properly or the knuckle to barrel hook is worn. I am sure a gun of that age with the rust it has a visit to a capable gunsmith for a well needed repair estimate and service, would be worth your time and trouble to know of any hiden problems as well as the rust.

The only lessons in my life I truly did learn from where the ones I paid for!