I, too, have never seen what sure looks like the diode and voltage taps on the outside. It almost looks inside out. Very bizarre. And I agree with humber that it might have been modified. Then again that mounting plate looks well done, so who knows. If I were you I would search Google Books (not Google) on 'Sears Meteor Battery Charger' to see if you can find an ad that shows what they looked like. And if you want to see learn more about and see examples of other diode rectifiers, in general, click on the 'Battery Charger' links in the Index in the Sticky.