1st thing, 26" is too low for the SPF, IMHO. recommended is 27"; I have set mine (with 17" wheels) to 26.75" all around. With 26" your camber will probably have too much negative and may need a major adjustment.
What motor is in it? With a small block, the springs up front are usually 375lb and 10", and the rears same rate but 12". With my big block, fronts are 425# 8" and rears are 225/475# variable rate and 10".
If adjusters are all the way up, your springs may be too soft but I doubt they would be different rate springs L to R.
I suspect you made the adjustments with the swaybars on. Adjustable rate shocks should be at their softest setting. Swaybars should be disconnected, and then when your ride heights are good, reconnect them tight but with as little preload as possible, and then reset the shocks as needed (halfway is a good starting point then check the ride) Also, make sure you bounce and roll the car after making spring adjustments.