anti-inversion shackles are particularly useful on the rear when ascending or descending obstacles with wide flex
hang onto your normal shackles, they are useful on the front (or you can sell them later)
in this line of trucks, you'll just have to get used to accumulating parts that you may or...
if you intend to wheel the truck, a U-bolt flip kit will just turn the U-bolt upside down relative to the springs
this will keep the U-bolt ends out of the rocks - look at the spring plates and it will become obvious to you what a flip will achieve
with no intent to cut into @lcwizard's (4Plus.com) market on 40 shackle reversals, but honestly, you can a buy a whole lot more useful stuff from him for the money - U-bolt flip kits would be my first suggestion, beefy bumpers, anti-inversion shackles . . .
much discussion on this to be had here in the 40 forum if you search back enough
having wheeled Moab in a manual steering '72 40 for 10 years (4" lift on 33s back then) and not ever having encountered a situation where fixed vs. moving shackle location would have made a difference, I don't see...