Instructor Wing

[mtnman]

I recently acquired this Instructor wing which has been adjusted by the pilot instructor to be free of the divot in the center where additional DI could be soldered. It looks like he had the jeweler take the divot out and then solder the two wings together to form and clean contiuous wing form. You can see the variation of this wing in More Silver Wings WITH the middle divot and a slight difference in the wing design on page 322 top photo. What era are these from? They are just a bit over 1 1/2 inches.