The Haynes manual contains about 85% of the info of the factory manual. It's less than $20, and much more easy to carry. (And when I say it contains the info, I mean the exact words and photos from the factory books!!)
Tom Wilson's "How To Rebuild Your Volkswagen Air-Cooled Engine" contains sections on the 914 engine, and is an excellent resource. One or two bits are confusing (come back here when you try to get the cam gear timed to the crank gear) but it's very good overall. Jake Raby over at
http://www.aircooledtechnology.com has an engine rebuild video that shows what goes on in an engine rebuild that has no "gotchas".
--DD