The Complete Porsche 912 Guide (3rd Edition)
Now in it's second edition. A great, well probablly the best 912 book ever written. Something for everyone, from the casual reader to the engineer. Chapters on performance engines, maintainance and all kinds of useful information for the 912 enthusiast.
Buying Driving and Enjoying the Porsche 911 and 912 1965-1973
James E. Schrager
Another classic from RPM. This is a great book for every 911 or 912 fan. Something for everyone, a true bible. James has written many Porsche books and is well known in 356 circles, more facts than Wikipedia.
ABC's and 912's...
Out of print
Harry's magnum opus.
The Bible for 356 and 912 engine builders.
101 Projects.for your Porsche 911
Wayne R Dempsey
MBI Publishing Company
Great project book aimed at the 911, but most applicable to 912. For the technically minded and the practical owner.
The 911 and 912 Restoreres guide to Authenticity
Dr Brett Johnson
Beeman Jorgensen Inc
Details of every inch of every year, enlightening stuff for the detail and concours Queen, engine/chasis numbers too.
The original non Porsche manual, published in 1969, Lovell book is practically identical.
Haynes 911 Restoration Manual
Lindsay Porter/Peter Morgan
Basic but thorough 911 book, many things applicable to 912.