Here is the link to Speedway Motors,
http://www.speedwaymotors.com/p/2079,,_Spring-Liners.html?itemNo=spring%20liner
and Yogis Inc. ,
http://www.yogisinc.com/Detail.cfm/-/Product_CD=2642/product.htm (they offer more sizes)
I did all the work myself. You will need new center bolts, NAPA, trailer supply, spring shop,
aftermarket truck supply house, or general hardware store. You will need a grinder or heavy duty sander to remove rust and sharp edges. And you will need to be able to bend the spring clamps so you can get each leaf out. You will want to paint them when apart, so get some black paint.
I rounded each end of the springs so there was no sharp edge to dig in to the poly liner. It won't take much or to long to do, then give them a quick sanding or grinding. They are so hard, you won't remove much if any material. The poly comes in 20 ft rolls, cut full length strips making sure you cover the ends of each leaf. I used three rolls for the whole truck. You may want to do a quick measure to see approx how much you will need. Yogis was a little better looking, but Speedway has great shipping to my house so I bought from both. I put the lips facing down over the spring so they wouldn't catch water and dirt.
Use C-clamps to pull the springs tight, the center bolt is just to hold them once tight. They are made from soft material and will strip easy when tightening. I used a allen head bolt in the front springs of mine since they were so short. Just make sure the head of the bolt will fit in the location hole of the axle. Once the bolt is tight, cut off the extra and use a hammer to flatten the remaning threads enough so the nut can't work loose.
I use a torch to cut the old center bolt, but a hack saw or wrenches will do the same. Have a C-clamp on so they don't go flying. They won't go far, just don't have your hand right in front. They are not like a loaded coil spring, but still require respect!
This would be a good time to check the shackles and pin bushings, clean out the grease fittings, and get new gasket/seals for the shakle pins. I would also consider new u-bolts. If yours come loose easy, clean them up and reuse. If you fight them, for sure replace them.
Joe