Hi FemaleFan, Buzz here. I didn't know what kind of airfoil was installed, i remember hearing the story of the 4% leading edge extention.
Every so often we would install a stainless steel patch to repair leading edge . Stainless steel patches were able to be made thinner than the standard aluminum patch. That was back in the mid-80's so the details are getting kind of fuzzy.
I have a book on my bookshelf, "The Big Eight", it's some of the story on designing / building / selling the DC-8 but is kind of light on engineering.
it's a nice day to go flying here (near Portland Oregon) so i'll borrow my friend's Champ and fly with the windows open for awhile.
Buzz Fuselsausage: Line Mechanic by night, DC-3 Crew Chief by choice, taildragger pilot for fun.