Chassis Stiffening

So I decided to build an autocross car. Been thinking about it for a while and decided to start planning the build. Think it would be fun to take out a classic car for some track time on a road course. I want to keep the stock type suspension, aftermarket control arms etc. but keeping torsion bars.

I thought it would be cool to us my Barracuda for this project. But I remember someone choosing a notchback Barracuda over a fastback; because the notchback chassis was a little more rigid because of the bracing behind the rear seat. So in my case since I have a fastback Barracuda and a Duster. Between the 2, the Duster would be the better platform to use because of the extra bracing.

But anyways, so my plan is to stiffen up the chassis but to minimize the weight increase. I'll make a list of what I was thinking of adding to stiffen up the chassis. If I missed something or if there is something is better please comment.

Welding up, gusseting, and reinforcing K-frame (almost no weight penalty)
Front and rear torque boxes
frame connectors
core support stiffener

Now I was thinking either a brace between the shock towers and the firewall, or US Car Tool inner fender brace, do they accomplish the same thing or 2 different areas and should use both.

Any other suggestions?