Nico,

You might get more correct responses/advice by posting part numbers and/or links to parts.

Fender welt goes between fender and cab-side.
https://www.chevsofthe40s.com/detail/6530/Chevrolet_Fender_Welt_14_X_1316.html

The "anti-squeak" might go between inner fender and outer fender?
https://www.chevsofthe40s.com/detail/6533/Chevrolet_Fender_Gasket_Set_Inner_Panel_Front_Fender.html

They are both standard/necessary parts.