Here are a couple links through our friends at low and no-tech magazine http://www.notechmagazine.com/farming/
The Agricultural Building and Equipment Plan List
"The University of Tennessee Extension maintains a collection of over 300 building and equipment plans, and all are now available in electronic format for download. The plans are primarily intended for use in Tennessee, but many are appropriate for other locations as well. http://bioengr.ag.utk.edu/extension/extpubs/planlist97.htm
Also on Archive.org to add
Handy farm devices and how to make them (1912) http://archive.org/details/cu31924080109832
http://www.antiquefarmtools.info/page5.htm
http://www.princetonimaging.com/library/mechanical-dictionary/
http://www.mot.be/w/1/index.php/IDDOCEn/ByMorphologicalUnit
http://www.princetonimaging.com/library/western_electric_catalog_1916/
http://farmhack.org/wiki/how-manage-balancing-college-and-everything-else