member "hot rod deuce" can help best, as he's modified his to accept 16x20's <img src="emoticons/icon_smile_approve.gif" alt="Approve">
but, stock they won't fit. You'll need custom springs and longer bogie arms, and a longer driveshaft at the least. That's the main stuff, the front axle can probably stay in the same spot, get longer spring packs, or at least a couple longer leaves to combine with your old spring packs (might not hurt with that extra lift), custom driveshaft, and lengthen or fabricate new bogie arms. New longer brake lines may be needed for the rear axle.
Probably need wider custom wheels as well