I think I am missing the round aluminum pieces that make up the wing
The spars. They are 13.5 feet long. People often store them up in the rafters of a garage or shop.

Photo #29 is the four I beam inserts for the spars. One for each spar.

It looks like there is a firewall forward kit for a Rotax 912 included. Ring mount, prop, exhaust, cowling...

The welding on the fuselage wing strut attach points was probably to install a rod inside the strut carry through tube to increase maximum gross weight rating.

Near the front of the Builder's Manual you should find a "Parts" section. It will have a detailed listing of all the parts included with this kit. A buyer...or other person...that is familiar with Kitfox should be able to use it to do an inventory.