Tech's advice is sound, and no, you don't need both. As Tech stated, the Original Factory Service Manual is
Quote Originally Posted by techinspector1
Written for Chevrolet Dealer mechanics by Chevrolet Motor Division of General Motors.
while the Haynes, Chilton, etc are like a Reader's Digest condensed book - they take the Original Factory Service Manual and pare it down, taking out step-by-step instructions and replacing with "Here's a picture, take it apart, replace the gasket, and then reassemble in reverse order" where the OEM book will give you exploded views of the parts, and point out that you have to take off part A before part B will come off. Buy the big book, and enjoy the instruction it gives.