Looks like the post binder ears need some attention too
Good project for learning on a few levels.
One path would be to do an alignment (with the LH dropout location left "loose", alignment based on RH side that's still intact) then install in a jig to have geometry trapped so to speak. Do one aspect at a time, replace or fill the tube/dents. next replace/reattach the LH SS. I hope the seat lug was done with brass/bronze as this will make the repair of the lug ears easier. Andy