lowering all wheel drive......

i know i've heard all the crap about how not to attept to bag a 4x4...but i got a customer that wants his all wheel drive blazer or bravada, which ever it is, lowered only and i told him that you can't get too low with the all wheel drive. i'm just wondering what to tell him on how low it can get, he wants to know like specificly, so i was wanting some input on how-to and how low i could get it for him. any help would be great. lataz.

if ya need to know more lemme know