Is there a formula for picking the correct spring for a DA Coil over spring on a 4 link or ladder bar car?
How do you know if I too stiff or weak?
What are the symptoms of he wrong spring?
Just got my sons' dart ladder barred and need springs

If you know the rear weight there is a formula...
rear weight of the car minus the rear end... then its
a matter of your shock length.... most A=bodies will
be in the 120# per inch... set the lower spring adjuster
1" up from the bottom ... if it has to be moved more than
a inch either way to get the shock to its design length
then change the springs... use just enough to hold the body
up

There will be a number of different rate springs that will support the weight of the car at the correct shock installed length. Which one you use is a tuning decision. The 120-130# number mentioned is probably the right baseline spring. Starting with the spring seat 1 inch up will give you a good baseline. A heavier rate spring may require the spring seat to be wound all the way down. A lighter spring can require the seat to be wound up a couple or 3 inches. A lighter spring will store more energy than the heavier one. This can help with getting the rear out and the tire applied if needed. Some people opt to go this route and control the separation with the shock, especially with a 4-link car. Keep in mind, the shock has a specific installed length that needs to be maintained. Winding the spring seat up or down to adjust ride height is incorrect. Too heavy of a spring results in the shock length being held too long with the seat all the way down. Too light and you crush the spring to or near coil bind to hold the car up at the correct shock length.