I was hoping that some suspension experts would have replied to your question ... I'm interested too.
The first step is to get the car corner weights, travel calculations, etc.
Many sites have information on how to set up a suspension, see QA1 link.
http://www.qa1.net/qa1_motorsports/images/drag_tech.pdf
My Cutting Edge Replicas was set up way too stiff. Bounced over small bumps and felt like a skateboard. Brought to a suspension shop and had it frequency tested. The frequency was very stiff at over 2 (close to Formula 1 car frequency!). Long story short, new Koni's, new springs (rear 600 to 450, front 500 to 350) 2-1/2" to 2-1/4", very drivable now. $$$ ouch!
I've also got a Shelly Valley Daytona Coupe that was set up for the track and the suspension was way too stiff for weekend driving. Great on a smooth freeway, but too stiff for potholes.
Had 450 front (with anti sway bar), 350 rear. I am now running 325 x 10" on the front with new QA1 double adjustables, 125 x 10" on the rear with new QA1 single adjustables (just added last month). Probably should have 8" on front (recommended length for shock) and 12" on rear (long travel shock, recommended spring length - didn't have any 12" springs), possibly 150 rear. Rear 125# spring compresses ~2" at rest, no preload. Getting close and much better. Will need to test drive more.
Longer springs and no preload? Add preload to current springs? Check the recommended spring length of the shock. corner weigh the car, check wheel travel, then buy a bunch of springs! eBay! Or bring to suspension shop and pay the $$$?