Here are a two sources for you:
"Grand Central - Gateway to Millions"
By John Belle and Maxinne R. Leighton
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
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:
... and probably at the New York Public Library.