Steve,

thank you very very much. Height difference appears to be about 1.5mm on either side measured from the centre line at the trailing edge of both stab halves. I'm probably going to cut the balsa bevel I previously sanded and replace it with some balsa in order to sand it on the other side. Luckily I didn't install plywood reinforcements on the under side (now upper side), so it won't be a big problem, just more sanding... Luckily also that the moving parts are almost equal, so little work to adapt it to the "wrong" half but no cutting and sanding there.

This doesn't yet solve the problem: where is my "dihedral" coming from? I don't think that the folks at CA changed the way the halves are built, so I guess one (or both) of my stab halves has some sort of error. I will make more tests with my stab and search for the root of the problem. I don't think it is a big issue, but I'm interested in knowing what went wrong and where.

Thanks again for your help, thanks!
-Fabrizio