When I built my ERA, I planned to run "Open Track" and autocross events with it. I added extra bracing, to provide protection and stiffen the chassis. My modifications were "home-brewed", and not done to any particular sanctioning body's specs.
1) The decorative bars coming down at the front of the tunnel, which, on an ERA, only mount to the tunnel, I had fabricated out of thicker tube material, and lengthened them to bolt to the chassis (and bolted to cross-bar #2).
2) I had a bar mounted across the car, behind the dash, that is welded to the door pillar supports on each side.
3) The side bar braces are welded to the door pillar posts at the front of the door opening (tied to the cross-bar), and to the frame and original roll bar at the rear.
4) I ordered the car with a roll bar, braced to the rear, like a 427. I then added a forward brace to the roll bar like the 289 style.
Hope this gives you some ideas.
regards,
Jeff