Not fenders, but if it helps at all, here's some photos of the different types of material (or remains of) from an NOS front shell for the 11 cab. I guess the 'fabric' type would be used on the 13 cabs, when rubber became harder to obtain? Note the black residue (tar?) used to seal the fabric type to the metal.....note also that the fabric has a textured outer finish, similar to the 'grained' products listed here:
https://www.vintagecarparts.co.uk/se...ry=Wing+Piping
Owen.