Do I need to add the LCA braces?

If you car is an original 67 383 GTS I would definitely not weld those plates on your lower control arms.

Very small gain for a lower handling performance use. And I would try to keep the non original stuff on a car like that all bolt on and removeable.

Yes good point. Only has a few bolt on things and is an original 67 GTS that has been mostly restored. A few more things to do.

Has build sheet and documentation from Chrysler Historical. Car was purchased from Grand Spalding Dodge aka Mr Norms. I got it from the original owner when it was about 1.5 years old. Second oldest 67 GTS on the the registry.