Ooh very interesting. Good job on stripping it back ed. I'm thinking it would be best to remove the complete down tube. Then the top tubes can be straightened and the head tube angle reset. Then weld in a new down tube. I'm thinking it would be better than lugging it as there isn't much tube to lug.
The drop outs could be filled with weld and ground down. Or new ones made up. But on the whole I don't think it will be to hard to restore this frame into a good condition rider again. The only problems are if it is twisted anywhere.
