In a book called Fokker Fighters of World War 1, by Peter Grey and Ian Stair, from 1976, the DII and DIII drawings show the same chord, about 16.5 mm each, which is 118.8 cm, or 3 ft 9 ins. I'm NOT challenging anyone else's figures, but it is interesting that what should be an easily defined/measured figure has so many variations.
One would need to know how the different artists/draftsmen came to their conclusions. Are/were there accurate original measurements available somewhere? Profiles of D II and (incorrectly labelled) D III on page 24 of Osprey Early German Aces seem to be about the same. It's an interesting little conundrum.
Cheers, Russell