I saw you post, and I thought "oh, shit, I am about to be schooled by the mechanical engineer." I agree with you in a lot of ways, though. However, the support near the dash sits a little bit lower and a bit further back. There is no cowl support, from what I have seen. There is, however, a beefy bar that holds the dashboard in place. This might be a viable alternative.

Mind you, this is all moot, in my opinion, as I don't think that any single bar can have a huge effect on torsional rigidity. I think that the primary purpose of a shock tower bar would be to keep the shock towers parallel. I don't think that anything short of major chassis modification or a roll cage would have an appreciable impact on torsional rigidity.

But, back to the firewall question, Here's a pic with the cowl removed. It's kinda big, but it shows the structure of the wall. I don't think that there is anything back there that would take the deflective load with any strength.
http://www.theta.net/nichols/newengdsm/mberte/DSC02709.JP G

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