A-Body chassis bracing- stock and aftermarket- what's good?

I have noticed that some A-Bodies (usually '73+???) have some bracing under the hood between the inner fenders and the firewall.

What is the story with these braces? Are they any good? Was it part of a package?

I'm also looking to add some bracing to my 'Sport as it gets closer to road-worthiness to alleviate some of the fatigue of old age (and flaccidity of old tech)...and hopefully make the whole car drive better.

What's a good place to start?

THANKS!!
-Mike