Different springs are only part of the lift. Don't forget about control arms, track bar, brake lines, etc. Also, doing an SOA using your 2wd leafs will net about an inch less than what a 4wd would, meaning the amount of lift from stock is the same, but 4wd will sit ~1 inch taller. So a 4wd doing an SOA will need 5-6 inches up front to match, you'd only need 4-5.