Keith,
Many thanks for your thoughts and a few new "angles" on this little quandary. When you add all the points up it is almost irrefutably a Fokker Built Merc powered DVII. The beautiful clear photo of Sachsenberg and his dog on pg 56 of Vol. 3 refers to the aircraft as "his spectacular DVIIF" as does the Coloured Plate and info on Pages 34-35. The other two photos of the machine on pg55 refer to the aircraft as a Fokker Built DVII. It could easily be a simple error or a slip in the editing process.
As for the louvres there is, IMHO, no standard layout(s) that we can really hang our hats on; once into the Field it was every and any layout that would work!
The black rectangles appear to me as a glue, dope, or extra panels of fabric to prevent delamination during high speed dives or extreme manoeuvering. I read this theory, I believe, in the Instruction Booklet.
You are right, this is half the fun of it. I'm still not sure if I will do this scheme, but the overall effect is very tempting!

Cheers,
Lance