Is the bronco used for strictly offroad? If it's strictly offroad i would say yea, 4.56's would be good, but if you do any highway driving, your motor is going to be screaming and you can say goodbye to your gas mileage.
If your going to use it for offroading and street use, i would suggest you go with 4.11`'s, this will ease your motor on the highway, and keep you with somewhat decent gas mileage.
When changing gears, you ALWAYS change front and rear, or you will never be able to use your 4x4 again. The drivetrain will bind from the different gearing, if you go with 4.11's you need to go both axles.
There is a sticky on this, i suggest you read that, and try a search for gearing, there is a lot of information in this subject already.