You can have lumber wagon stiff springs with out raising the current height of the car. You would need to have custom springs wound for your car (less expensive though a lot more time consuming that having a custom cam ground). Eaton or Moog would need to know your four corner weight, (you will have to borrow a set of digital scales from a local circle track or road racer; or a DOT cop, and then place one under all four wheels unless you want to spring for $1,200 for a scale for your garage). You can approximate it by driving half on a truck scale at the dump or at a truck stop (CAT Scales charge $7.50 an axle unless you don't want a print out in which case at my local truck stop she says it's free). Then you have to determine what your current ride height is (all that takes is a tape measure, but it is best if you measure at the same location the factory did with this info being found in the Chassis Service manual, or the Fisher Body Repair manual). Then they want to know how stiff a ride you think you need to perform in the manner you intend to drive it. The faster the sped the stiffer the springs have to be.
That takes care of the springs, which just holds the car up. Shocks with the correct linear travel to match your suspension are the next item on the list. As you lower a car from the factory ride height you shorten the amount of time the shock has to respond because as you shorten the effective length that the shock travels as it follows the spring it takes less time to go from at rest to compressed. So the faster you drive the faster the action the less time between compression and rebound. The shocks can be mono tube (factory original), or twin tube when considering a gas over oil shock. Valving can be fixed (the 90/10 or 50/50 from the sixties) or variable by adjusting an orifice and a needle to fill the orifice which controls the rate of fluid transfer from one cylinder to another. These adjustable shocks can be single or dual adjustable. The single controls compression or rebound depending upon how you mount it, or it controls both compression and rebound offering 256 different settings to tune the suspension to the track.
You can also add or enhance the amount of body roll the car experiencing with stiffer (bigger and stronger) anti roll bars that are just auxiliary springs. Changing the length of the distance from the pivot point to the ball joint (requires replacement A-arms such as tubular A-arms, or rear control arms also affects the steering geometry and Ackerman angle with rear control arms). Heightening the steering knuckle(distance between ball joints) allows for bigger brakes as well as improving steering geometry ion some (not all) cars.
Of course making the frame stiffer only helps performance, but the only bolt in is a brand new frame made by a frame builder. Though people have attempted to brace and reinforce the old X-frame by plating the torque box to stiffen it up as well as enclosing the open C-channel by boxing it in. The only competitive solution is a brand new frame.