Very nice work GD!
Dimensions according to Breyer's "Marine Arsenal Band 22 - Die Schweren Kreuzer Der Seydlitz-Klasse"
LOA with straight bow 207,70m CWL 199,50
LOA with atlantic bow 212,50m CWL 199,50
Breyer states Gröner and Koop & Schmolke as a source.
The above mentioned dimensions are identical to Prinz Eugen, which kind of makes sense I guess.
Edit:
Paul Schmalenbach gives the same data.
When I worked on the cruisers (and I still plan on updating my drawings from back then...) I planned on using the lenghts from the Marine Arsenal as well. It feels strange that it would have the excact same lenghts as Prinz Eugen, as Seydlitz was another (sub-) class, but I though that was as close to a correct lenght as it could get.
By the way, that drawing looks great!
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Any help and source material is always welcome.