Stephen, that is a difficult question!
I checked my book "German Aircraft of the First World War", but it contains only your second picture, no drawings or sizes.
You mention a engine "150hp Benz IIIa". I think the a is wrong, today Mercedes-Benz is one, but at that time there are different engine lines:
- the Mercedes D.III 160hp (and D.IIIa with overompression and more power) - not used here
- the Benz Bz III with 150hp, used on this plane (there are more developments of Bz IIIb and Bz IV, which I showed as mode here)
There is a article with sizes on Wikipedia, your
Gitterschwanz is mentioned, but also the OAW (Albatros) C.II. So I do not know, it the dimensions are correct.
https://en.wikipedia.org/wiki/Albatros_C.IIMay be you find some source, that wings are taken from another Albatros type - that would mean you can use that as base to recalculate the other dimensions.
Sorry, could not help further.
Cheers,
Frank