i've done a body lift on my 300. 'cos i wanted the height to accomodate bigger tyres without altering the suspension geometry
first wash the under side, you'll be cursing if you spend the day with crud dropping in your face trying to shift bolts.
the seatbelts all mount to the chassis, the clevis pins under the boot floor are the most problematic as access is restricted and it's hard to get a torch in there if you need to burn them.
the transmission tunnel rubber gaiter will need to be drilled out or run the risk of damaging it. check it is in tact or buy a second one, and canabilaise the first one to create a seal gasket for the top of the gearbox. do this before you go wading again!
you will need a friend with a lathe to make you some radiator mount extensions, and a gear lever extension for your transfer box. dont expect your gear levers to work correctly until you've moved the positions of the gaiters very slightly, i had to dremmel out the center console and move the gaiters backwards.
be prepaired to cut the bolts off or torch them on every mount. out of the 10 bolts that hold the body to the chassis only 1 came away clean without heat or grinder.
expect your steering to feel a bit wierd, the extra travel on the linkage puts a slight new angle on the UJ's and forces a noticable center spot in the steering , check the power steering resevoir the uplift may stress the hoses.
check the fuel lines to your fuel filter from the lift pump, they may be over stressed by the lift. (my mates sheared due to this, but then he had just decended chapelgate, which is enough to break most cars)
fit extended brake lines.
altering the bumper height... i havent botherd, but did need to modify my rear heavy duty bumper slightly by cutting out to make it fit .