Dont qoute me, but I beleive to fix the lean u actually need a lift shackle out back of 1"...someone else will chime in.
However, If you do cut coils, do a bit at a time. Both my red and white rcsb have trimmed coils. If you cut about 1/2 a coil off a nbs spring for a RCSB it nets you about 1"....at least both my trucks where like this. Be prepared to put it in and out a few times