When it came time to shim between the rear longerons and the longeron doubler with a .040" shim, that just wasn't enough. This is because my bottom longerons from Tom H. were made with .125" extruded angle rather than the .093" specified in the plans. This is an acceptable substitution, just a bit heavier. I ended up making more 100mm .040" shims so I could double them under the doubler. No harm, no foul.