the flex on leaf sprung vehicles are also helped by not using (or undoing) the spring retainer for the leaf-pack, allowing them to separate like this image from 5lam...
(which is the reason the leaves separate, and probably the only mod that some owner in the past has done...)
Other things that assist with flex on leafies, shackle angle at 45 degrees, and for gods sake, check the pins on the shackle... With them done up too tight, you just end up binding it all up...
When looking for a perfect length shock, remove the shock completely, then lift and measure what flex you can get and buy accordingly the right shockie
Hope this helped, been a while since I was in the old bone-rattler
