I've done the following
- The Don Rome STB set with the Dimpled SS front bar to clear the LS4 V8 alternator. Made a bigger difference than I would've thought.
- Addco 639 rear swaybar with Moog K6662 end links and 7/8" (22mm) Moog K90397 Poly bushings with the GM straps lubed with Sil-Glyde. The squishy rubber bushings that ship with the Addco bar will eventually break down and the steel sleeves will slam and clank against the rear crossbar.
- The Dorman 927-101 front swaybar with Energy Suspension Poly bushings and Moog End-Links. The bushing part number is in the LT1-tech W-Body suspension thread. It honestly didn't seem to change much but the old one was cracked at the end so it had to go.
BMR, UMI and ZZP-Performance still sell tubular lateral and trailing arms. The lateral arms usually have adjustments on both arms... not just one. Some only advertise compatibility with the Gen VII Impalas. The rear trailing and lateral arms fit the Gen VII and Gen VIII chassis.
Since the rear arms fit the W-Bodies from the 90's til the end... they may not disappear as quickly as parts that are a bit more model specific. They will go away eventually tho.
Rear swaybars are a bit more difficult since they tend to be more model-specific. Worst case you can at least upgrade the LT, LS and Base Impala to the FE3 Impala SS or the FE4 Monte Carlo, Buick Lacrosse Super, or maybe the Pontiac GXP rear bar.
I've purchased the BMR lateral links and the UMI DOM (Drawn Over Mandrel) seamless tube trailing arms for later upgrade.
I've also bought Moog Variable Rate springs and Buick Lacrosse Super Bilstein Struts so I'm gonna have a suspension party in the barn this spring.
The Impala SS and Monte SS are a Buick Super 3,700-ish lbs curb weight. The V6 engine Impalas are closer to around 3,500-ish lbs so the Pontiac GXP struts and lighter rear springs are better suited for those. Look at the page two posts on the KYB AGX thread where it skewed slightly off topic into springs and stock-ish Bilstien struts...
If you're on a tight budget and have the FE1 or FE2 stamped sheet metal trailing arms instead of the solid "SS" FE3 or FE4 solid trailing arms you can probably find used "SS" trailing arms for a pretty reasonable price. They will help some but not as much as the tubular arms. I'm likely to be selling mine later this year... I have the old 2009 SS swaybar stuck in the rafters of the barn with a scribbled-on toe tag too.
Don't overlook the brakes. You can go to the 12.7" stock 2012 "cop brakes" with lots more surface area for not a lot of money. There are several recent threads. I'll probably make my own when I finish this round of upgrades later this spring.
I finally got rid of those miserable Goodyear Eagles and installed a set of Michelin Pilot A/S 3+ 235/50ZR18 97Y tires that will actually have rain traction and will hang onto the corners. The W tires would be just fine but the Y rated tires pretty much fell in my lap for a pretty decent price.