Where can I find drawings or diagrams of the Boeing 737-800's internal layout? I am working on an alternative fuel system for my final school research. I am applying it to the 737-800. Now I could not find info on how the internals are situated. Of course pictures of the cabin are widely available. However I am looking for drawings, pictures or graphs on the cargo compartment, systems placement like gear, hydraulics, pumps or whatever. Basically the whole internal volume and what it is occupied by.

This is maybe a bit demanding but any info is really helpful.
Check out the "Airplane characteristics for airport planning" document for the 737, espcially from page 47: http://www.boeing.com/assets/pdf/commercial/airports/acaps/737.pdf 

These kind of documents are created by the airplane manufacturer and are often publically available.