Bruce Andersons "Porsche 911 Performance Handbook" ISBN 0-87938-269-4 The BIBLE to building 911SC and earlier motors (and suspension upgrades). Try to find this first edition (look for the sticker on the cover that slipped by the proofreaders). The second edition ISBN 0-7603-0033-X is the same as the first, with updates to 1996.

Also visit Rennlist.com http://forums.rennlist.com/ the forum for Porsche. There are entire sections for the air cooled cars (what other Porsche is there ) and Performance and Competition.