Fitting is pretty straightforward and can be done with the car on axle stands. You will either need to buy new bearings or re-use the old ones. The inner races are an interference fit on the diff so need a puller to get them off. I managed to do this quite easily with a small 2 leg puller, but even if you need to get it done at a garage it will still be a lot cheaper than new bearings. The bearing pre-load needs to be adjusted on reassembly - its the same principle as adjusting a wheel bearing, not too loose or too tight. This shouldn't be confused with the preload on a RWD diff where you are adjusting the depth of engagement of the crown wheel and pinion gears which is generally a lot more critical.