Need some help with coil spring replacements

[FLYNAVY30]

It has become apparent that part of my covered wagon ride quality is due to sagging coil springs. The rears in particular have multiple coils touching with the weight of the truck on the ground.

My Suburban is a 1972 3/4 ton C20 that came with the 402 cu. in. big block. Looking at the specified replacement springs from Moog:

Front: 6104 constant rate

Rear: 6101 constant rate
6103 constant rate heavy duty
CC603 variable rate
CC615 variable rate heavy duty

So with only one option for the front, that decision is quite easy. My question is, what are the proper springs for the rear to match the front? I'm assuming the HD springs would be used in a truck that saw frequent heavy loads or towing? I'm also not sure variable vs. constant rate.

Any input would be greatly appreciated!

Thanks
Greg