Aside from the caster/camber interdependence, the Mopar design was and still is very good.

Welding up the K frame resolves a few other issues than simple engine bay flex. The K is the primary loaded structure in the front end. With supporting the engine, steering box, and the front torsion bar/control arm anchors as well as being spot welded together, welding it up provides a big boost in rigidity to a number of components in addition to the front section of the car.

Because the upper control arm mounts and shock mounts are not radically loaded in a mopar, the shock tower braces is less about providing loading support than it is of increasing the rigidity of the simply cube structure that is the engine bay. By turning it into multiple smaller triangles, you can reduce the flex. Percentage of improvement by doing this, I can't quote a number. Because of the lack of loading in the upper parts of the engine bay, mounting a brace to the firewall can be effective in a mopar, but there is a question in my mind about putting structure that mounts in a large flat plane of sheet that doesn't make me think it is the most effective way to do it.

I read a white paper on nascar design sometime ago. In it they stated that the most heavily loaded area is the firewall/a pillar area. While we aren't running out cars are near 200 mph speeds on superspeedways, it does seem logical to say that improvements in this area on a performance street car can yield gains as well, especially since we lack all the triangulation structure they have in this spot.