Yeah, Tom Wilson's How to Rebuild Your Volkswagen Air-cooled Engine. http://www.amazon.co.uk/Rebuild-Aircooled-VW-Engines-HP255/dp/0895862255 Covers both type 1 and type 4 engines.
There is also Keith Seume's book http://www.amazon.co.uk/Aircooled-Engine-Interchange-Motorbooks-Workshop/dp/0760303142/ref=pd_sim_b_2/277-6846002-3194717