For technical diagrams, the first place to start looking is a dedicated online image stock or library, and the best free online image library is Google Images. I've just entered Google Images, typed in 'Ford C6 transmission' and came up with this diagram:
There were many other similar diagrams and cross-sections of Ford C6 transmission units, so if this one isn't quite what you're after, there are plenty to choose from.
If it's spare parts you're looking for, or a missing manual, or advice on repairs, try these online sites for help:
- ford-trucks.com - a forum for fans of Ford Trucks, where you can find posts made about C6 transmissions
- transmissioncenter.org - offers a blow-up diagram of the C6 transmission, as well as advice on all types of transmissions. Customer helpline: 1-888-2012066
- theoldcarmanualproject.com - has a full 1970 manual for the C6 available to print off
- forelpublishing.com - offers a PDF of the original C6 handbook to download
You could also try the usual auction sites, such as eBay, and if you're lucky, you'll find spare parts or manuals for sale. YouTube can turn up some tips, such as this film of a mechanic taking apart a C6 transmission: