1940 Pickup Panel Parts

[FlatheadEric]

A friend imported a deceased estate USA 1940 pickup into NZ that had been fitted out with 1968 Mustang engine and running gear, along with big and small fat wheels and tyres. It came with left over bits and pieces from its original 1940 pickup origin.
We have not been able to identify the two body panels in the photos. There is a left and right of both panels. The one with the criss-cross swage is made of fairly heavy gauge sheet steel.
Do these belong to an original 1940-41 pickup that are now surplus after the Mustang running gear and fat wheels were fitted?
Thanks for any help in identifying these parts.