I also have been researching this topic because it came as such a suprize that this was a view being put forth by the WT. In my journeys, I also contacted the archeologist in Jerusalem (see post by Lemans7), and this was the result.
My first email (edited to remove identifying info): "I have been trying to research crucifixion methods, in response to the teaching by Jehovah's Witnesses that Christ was crucified on an upright stake as opposed to T shaped cross (they claim this T shape crept into church history as a form of pagan corruption). Their sources are all from the late 1800s to 1940. (They quote W.E.Vine on the meaning of stauros, and an old article by a J. Parsons on "The Non-Christian Cross" which is available online at project gutenberg, however, I have not been able to find out who Parsons was and what his qualifications were for this article). I believe that more recent scholarship would show their view to be incorrect. I read with interest your article on crucifixion. Do you have any suggestions for where else I can look? Thank you in advance for any help."
Joe's response: "I get asked this all the time and my response is all the NT says is he was crucified, not how. Joe"
My next email:
"Thank you for a quick reply. Is it your position then, that there is insufficient archeological data to say for certain? I have not read the actual journal article, but I assume you have since it was footnoted in your article on crucifixion, but does the Canadian forensic science article on crucifixion seem to be well-done? It does address the issue of hands up over head as opposed to stretched out to the side. Thank you again"
I was referring to his article which refers to an experiment done re:crucifixion which showed that an outstretched arm postion significantly prolonged the time of death, whereas arms up over the head would have caused death in minutes. see
http://www.centuryone.org/crucifixion2.html
His reply: " We know from eye witness accounts from WWI and II that one dies rather quickly in that position. Joe"
I also found an online research article by [removed at Author's request], University of Hawaii
[link removed at Author's request]
There was also information at freeminds.org
http://freeminds.org/doctrine/cross.htm
I'm sorry if this has duplicated other posts.