Guess it depends on what you’re trying to accomplish. Do you just want it to be safe on the freeway in normal traffic or do you want to autocross? I wouldn’t put coil-overs on an otherwise stock car. If it’s bone stock… I’d probably prioritize this way (you can save all your original parts and can put it all back stock when you want to):
1. Wheels and tires – at least 15 x 7s with 60 series tires.
Better would be 17 x 8s up front with 245/45/17 and 17 x 9s on the rear with 275/40/17 (measure first-need around 5 inches of back space on 68-69 Buick A-Body).
2. If you have 4 wheel drum brakes, upgrade the front to disc and service the rear drums. (although 4 wheel disc kits can be had for around a grand, if you’re going to autocross or live in canyon country). Consider 2” drop spindles when you swap out the brakes.
3. Front sway bar, about 1 1/8”
4. Shocks – Bilstein (KYB if you’re strapped for cash) Good shocks make a huge difference in handling.
5. Tubular front control arms (upper and lower). These make a huge difference in high speed stability. No matter the manufacturer, the new tubular control arms allow you to get at least 5 degrees of positive caster. Factory style stamped steal cannot provide that range.
6. Replace all 4 coil springs. Don’t drop more than 1” with springs.
7. Rebuild steering linkage and replace the tie-rod adjusters with solid type such as QA1.
8. Replace rear control arms with quality boxed style and install an adjustable rear stabilizer bar, no bigger than 1”
I'd encourage you to buy Mark Savitske’s book “How to Make Your Muscle Car Handle”
Also, get a “Fas Trax” alignment tool and do your own alignment… after reading the above book.
Hope that helps. Enjoy the drive.