I am not a luthier, but I suspect that you will find that the design and the build approach has not changed very much. The old Italian basses from that period are generall considered to be the highest form of the art. Many luthiers are attempting to reproduce instruments of that caliber. You might want to discuss another aspect of the double bass, as was suggested above. Or you might look at regional differences in design, or some other aspect of interest. Try perusing the ISB website:
http://www.isbworldoffice.com/
I think that you will find good references there. Here is source for some info, including a thesis on the acoustic differences between flatback and curved back basses.
http://www.awbmusic.com/acoustics/index.htm
It will lead you to other references.
Jim