Gita chronology

[Hrid at aol.com]

In his book, "The Universal Gita", p xvi, Eric J. Sharpe states about the age
of the Bhagavad-gita:
   "As with all ancient Hindu scriptures, absolute chronology cannot be
arrived at by any means currently at our disposal; and relative chronology
can only give the wide range of dates which we have mentioned [400 B.C. to
A.D. 200]." Since in the absence of ANY absolute chronology, mere relative
chronology could not produce absolute chronology, even within a wide range,
and given that he has set the oldest possible date for the Gita at 400 B.C.,
I presume that Sharpe is here making an implicit, and customary, reference to
a fairly reliable absolute date for a non-Hindu, i.e. Buddhist, scripture.
 The most obvious and common example of Buddhist influence, of course, would
be the Gita's use of such terms as brahma-nirvaa.nam, found in the Gita at
2.72, and 5.24,25, and 26. 
   We also know, of course, that many Hindus will claim that such terms
demonstrate  Buddhist borrowing from the Gita; and that in any case Buddha is
an avatara of Vishnu, etc. 
   Be that as it may, I would like to ask the following: which articles and
books best present the relevant arguments used to date the Gita from both an
academic and a Hindu perspective? I have just begun my inquiry into this
topic, and my initial readings are a bit dissapointing.
   I am as always sincerely appreciative for any help in this regard.
Howard Resnick