Here are a two sources for you:
"Grand Central - Gateway to Millions"
By John Belle and Maxinne R. Leighton
ISBN 0-393-04765-2
W. W. Norton, 2000
- on page 61 you will find 3 track charts of terminal and approach tracks for G.C.T. Not sure what the date is, but I would imagine that not too much has changed. I bought my copy of this book, a few years ago, in the bookstore on the main level (west side).
"Grand Central... the World's Greatest Railway Terminal"
By William D. Middleton
ISBN 0-87095-071-1
Golden West Books, 3rd printing, 1981
pages 146-149 include very detailed charts of
the terminal tracks.
Both books are available on The Advance Book Exchange:
http://www.abebooks.com/
... and probably at the New York Public Library.