C-30 springs will ride rougher. Also if the truck is jacked up in the back it will throw off your alignment. Some big cities may have a SPRING SHOP that specializes in both leaf and coil springs.
The things to be concerned with are Outside Diameter, so it will sit in the mounting location... and the height of the spring.
You might could use C-30 springs and just cut off one or two coils. It all depends on how High you want the vehicle to set.
When you are done, check the alignment of the front and rear tires.
