I'm really confused about this myself. I plan on upgrading soon and I can't seem to get a good answer for spring rate. I currently have Mustang V6 springs and monroe shocks. It rides pretty rough with the low profile tires. I plan to switch to QA1 double adjustable coilovers.
QA-1 recommends a #700 spring which seems like it will be way too stiff. Here's a link to their chart and they list an average weight of a 47-54 truck.
https://www.qa1.net/tech/documents/S...le-Weights.pdf