I started to play with swapping front springs like you did, but right now I am living with it until I take him apart this winter for a frame repaint - paint is faded out after 25 years. It could be that the springs in the rear were swapped from side to side when we redid the truck many years ago. usually, the springs for the drivers side are a higher spring rate than the passenger side to allow for the weight of a driver and fuel if the tank is on the same side.