The shackles themselves are easy.
Go all the way to what they claim is the 4" hole.
It will only lower the truck about 1.5" at the wheel well.
No problem with shocks or bump stops.
The bigger job will be that you will need to spin the pinion angle shims around the other way.
Trust me, we have been through this hundreds of times on NLOC.
On the 03's and 04's for sure you will get a drivetrain vibration and chew up your u-joints if you don't.
You will need to undo the axle to leaf spring U-bolts.
The locator bolt runs through the springs and shim.
If you are lucky you can clamp the spring pack and spin the shims the other way.
If not you will have to loosen that bolt.
There is just a tapered pin head on the lower side. You will have to grab that with a pipe wrench. Vise grips will slip off.
Don't break the bolt! It's some weird size that cant be found. I think it's 11mm