the foil trick is a bit of a crock, IMHO. You can try some quality polish like Mother's, Simichrome, etc. But the oxalic acid soak will do it too, if you commit to the complete tear-down and rebuild. After a point, there's no bringing back chrome plating that's lost, if it's really pitted it will stay pitted. But some surface freckling can be removed so it's almost as good as new...oxalic acid does that job, and many of those non-abrasive polishes have OA as an active ingredient..
The SR derailleur should be able to handle a 26T rear cog...I like Zymol auto wax (cause it smells like a pina colada!), but any good wax works. Cleaner wax has an abrasive to clean off old oxidized paint. If you don't want that you must choose a NON cleaner wax (Mother's makes one, but these are hard to find).