Seems like I read here somewhere about the advantages and disadvantage of anti-inversion shackles. I'm installing 2.5" springs on my 40, considering putting on 1 1/2" extended shackles while I'm at it. What are the pros and cons of Anti-inversion shackles? I understand what they do, but I see many people that don't go that route. Also, when installing shims, are they required on all four perches or just on the front?