I recently did a rough country 4" lift on my 1985 K-10 SWB. The rear springs are 49" I opted for the heavy 1/2 ton 52"(3/4 ton} rear springs. I had to move my rear spring perches back 3". It's a bit of work drilling the rivets out lining it all back up. I welded my perches back in. I also have a Shop @ home, lift, welders, air, and Plenty of tools. I would have gone w/ 49" Springs 1/2 ton springs doing it in the driveway.My old suspension had tapped out before i bought the truck. If you're towing i'd opt for the heavier springs in the rear.Truck rides much better than it did.