I'm about to lift my 40. Its super saggy now. Should I go extended shackles in the rear while I'm doing the lift to level her up? Or will the new springs take care of that. Also, I've found some greasable stock length shackles for a good price, but it says they are for '80-later 40's Did they change the size fo springs and whatnot on the later models, or will the shackles fit a '79. Any help is appreciated as always.