Im looking at Front coil over conversion on my 83. i got spindles off a 95 gt and plan to buy a new k member and coil over conversion. not sure what spring rate would be best for the street. 300lbs and 400lbs. im stuck between.
If it's ONLY street driving you're interested in, I wouldn't go over 300, and depending on your struts and how aggressive you planned to corner it, I might not even go that high.
On my 89, with tubular K member, control arms, and coil overs, I run 250, and am perfectly satisfied with them. The best part of driving my car is diving into corners. Coil overs have a longer moment arm than the factory springs, so you roughly double their spring rate to equate them to factory location springs.