Very interesting thread! I recently bought the Trumpeter Schleswig Holstein 1935 kit and want to represent it as it was on September 01, 1939, when WWII started. As far as I have checked, the only differences are the location of the AAs (and I think the 150mm cannons, but I will use metal barrels anyway). Now back to the AAs, reading this thread, looking at the pictures and at the videos, I think I got all the single 20mm positions, but I am having issues finding out exactly where the 20mm C30 Flakvierling was located, just "...and one 2.0cm C/30 Vierling gun added to the port side-rear boat deck...". Any images available showing the Vierling in place? I have plotted the positions of the AAs in the image below, together with the pictures where I got the information from. The rear port 20mm needs an extension of the deck just like the one on the starboard side. The rest I don't think need any further work apart from replacing the structures in place for the aftermaket 20mm.
marco