You really need to check out this link. It's pretty detailed on rebuilding a 400.
http://books.google.com/books?id=WN...SPpcIH&sa=X&oi=book_result&resnum=2&ct=result
http://books.google.com/books?id=WN...SPpcIH&sa=X&oi=book_result&resnum=2&ct=result