Stiffening the framework Options

[Rand]

I'm looking into ideas to strengthen my car. Not a full cage, just a few tubes. I've read the classic threads and I'm in awe of the caliber of guys (like Brad, Jeroen, etc) we have offering help around here... hoping for your comments on this...

My goal is an aggressive street car that is strong enough for a V8 conversion. I'm looking for the simplest way to add some strength (with the least amount of added pieces). It's all about function and I don't need to be concerned with racing classifications and rules.

I'm thinking the first stage is bracing from the rear shock tower to firewall, then inside firewall to frame rail, something like the red bars in this image:

(IMG:http://www.4nets.com/baldwinpowersports/images/stronger1.gif)

Is the firewall a strong enough part of the structure to use this way (if the tubes are just welded to their respective side of the firewall)? Or should the tubes go through the firewall, welded directly to each other at the top, and another down tube tied in (like the green)?