Considering the "design" geometry, what do the replacement upper control arms change to make the existing geometry allegedly better?
If the car has factory a/c, I believe the FSM states it already has the "HD" front torsion bars (defined by bar diameter), as a part of the factory a/c equipment.
My recommendations? Start with ALL new rubber. Moog is a good place to look. I'd recommend against NOS as that rubber is quite aged by this time in its life. Do NOT do the final torque on the bushings (just barely snug the bolts to ensure they are placed and seated correctly) until the car is sitting at ride height on the ground. Do NOT forget about the lower control arm pivot bushing! Check and/or replace the rear torsion bar seals, repack as necessary.
Then a good HD shock at all corners. Some like KYBs, others like the higher-pressure Bilsteins. It's also been stated that the current valving is not the earlier C-body valving, that B-body valving is what's in the newer shocks. Not sure about that, just repeating what I've seen online. I'm not really sure that it matters as the piston diameter might have more affect than particular valving specs. Due to the architecture of where the shocks "clear" the front structure, the largest shock piston dia. is 1", but the rear shocks should be 1.375" pistons.
New sway bar rubbers, too. All of them (see thread on this). Possibly upgrade the rear springs to factory "HD" specs. Then the rear sway bar.
Also run the front tires at "+2psi" over the rear pressure. A little sharper steering response and a little more neutral handling, from my own observations . . . at your discretion.
From what I remember from when the cars were new, the B/RB engine cars were the best place to start, suspension-wise. Add the factory a/c option to get the stiffer front torsion bars. Front sway bar diameter was "a given". With 55front/45rear weight distribution, plus their better front end geometry, they cornered very good "as is" with nothing but elevated tire pressures. There was a reason the law enforcement people liked them so much! Add some good Monroe Super 500s (also used as the factory HD replacement shocks) and it was about as good as you could get anywhere. Even with the stock bias-ply tires. On our '66 Newport, when you turned the car into a corner, it was as if the car said "NO, I'm NOT going to lean!", resisting the normal physical forces in the process by cornering flat and responsive. NO other car, back then, felt that way to me.
The front sway bar was an option on the Slant 6 and 318 cars, but standard on the B/RB cars.
CBODY67