My
, I do not have a cucv, but I do have a GMC 1989 V3500 1 ton crew cab 454, same 80’s body style truck as your cucv, I went through reading tons of info and looked at all the companies leafs the number of leafs and spring rates for carrying capacity, flex and ride, my end result was a complete 4” 1 ton lift by Skyjacker with an extra fitted leaf that you put in the front pack yourself, it’s a main leaf with the ends cut off, so I have 6 leafs up front. I wanted to retain rear carrying capacity also so a shackle flip was out since it takes the leafs out of compression, plus my factory overloads wouldn’t work, but most have had good luck with the shackle flip, I have a block in the rear, and haven’t noticed any axle wrap yet but haven’t drove it a ton of miles since it needs tires. I also got the kit with hydro shocks, skyjacker dual stabilizer kit which I haven’t installed yet due to waiting to paint the underside of the truck, and drop pitman arm, I still need to do the longer brake lines, sway bar disconnects, and steering box brace, tires and more. , my opinion is it rides much better now, oh the skyjacker leafs have wear pads to, but when you add the fitted leaf it does not have any and is not drilled for them, also if you do have upper overloads they send you rear u blots not long enough but they have some long enough that they use with their 6” rear block lifts and you call them they will swap them for you, also on my rear dana 70hd I need to redo the shock mounts so they dont hit the axle tube with the shock body, thats why I dont have my pass new shock on the rear, I just havent got back to this truck to finish it. You can find a leaf spring rate table for 4” lift at ck5 just Google it. Hope this helps if you’re interested I will dig out my order sheet from 4 wheel online and get you the part numbers I ordered as that was a pain to figure out too.