[FirstOwner69]

I'm almost certain that the rear springs in my '69 3/4 ton were referred to as variable rate in the advertising materials when the truck was new. The ads touted them as improving ride quality when the truck was not loaded. I think that was the first time I ever heard of variable rate springs. A picture of one of my original rear springs is below.

If you click on the "info" tabs on the Rock Auto listings, you'll get all the specs for each spring regarding load capacity, etc. I have no idea which is closest to factory specs.