I pulled out my plans (Vailly) and compared the cross-sectional data in the book I have, plus compared with the view you posted, plus compared with the many photos I have and what's in the book. There does seem to be a difference, but nothing that can't be reworked if one really wanted. The straight longerons in the plans I'm sure are just considerations to structural integrity. After all, this is stick-and-glue, not aluminum-and rivet/weld. I can't find a specific dihedral angle given on the plans, although the plans are incorrect where they state the dihedral starts (a rib about 1/4 span out from the root). The full scale's dihedral starts at the wing root. I can't imagine dihedral being more than the full-scale, it's got a ton (2-1/2 degrees in the BirdDog book, 3 degrees in some Cessna references). Considerably more than most GA high wing planes. Mine will be honest to the full-scale, though, and I plan on some mods to the fuse anyway, so bringing the cross sections into line will naturally follow. Most of the models of the L-19 I've seen, including the Stafford kit, and probably all the ARF's, are built with too little dihedral.

The short blurb about the L-19 in this month's MAN mentioned that the builder had to relocate a former in order to make the scale door work correctly, so there are other differences as well as the longerons. I, too, like scale fidelity, but some considerations have to be made by the engineers/designers of these model plans to make them buildable by the majority of modellers. It's up to the true purist to change what they don't like, or just design their own.