4 inches is tough without some mods like Joey said, moving fuel tank is #1
also the clutch can come into play also, lowered seat bases and 1.5" drop and still move the fuel tank will get you close. depending on how tall you are, you might not move the steering or get a tilt wheel setup from doubletroublehooks???? can't remember who has them but Dorian probably knows.
Depending on where you are in your build or what you want to do, you can widen the frame/cage and drop them quite a ways, like the Magnum "milktruck" LOL