The rear leafs ride almost straight. Ford uses an angle shim beteen the spring & diff, you CANNOT remove these, as they set the relationship beteen the drive shaft & the pinion ( driveshaft/ pinion angle). Some trucks have a factory block. You can tell factory blocks as they have a wing sticking out the inboard side for the bump stop to hit. You can remove them & just have a spring recurved or changed out. If you do remove them, remember when ordering the new lift springs, you are at a -3", eg: 3" of lift wanted, 6" rear springs to be ordered. Frt. springs can just be ordered to the lift you want, then you must get an alignment, probably requiring an adjustable type of ball joint , to reset your camber angles. To get into bigger lifts on the IFS trucks you have to do extended radius arms, lowerd pivot mounts, alot of wk. It's easier to do a SFA swap. Hope this is the info you were looking for.
>-
this is the rear susp.on my truck . Even with the shackle flip I still need the factory angle shims.