Ron Downey, retired McDD engineer, has posted scans of Douglas factory display model drawings for the DC-1, DC-2, DC–3, DC-6, DC-7, and DC-9 aircraft on his blog: http://aviationarchives.blogspot.ca/
Follow the link in his blog entry to see a thumbnail gallery, then click on the thumbnail of the drawing you're interested in, then click on the "full size" link to see and copy the full size drawing.
There is a problem with the DC-2 download at the moment, and the DC-8 has yet to be posted, but I understand Ron is working the problem.
We all owe Ron our thanks for posting these. There's a lot of other good stuff on his blog, too!