4" to 4.5"

There are a few methods you can implement to go from the 4" bc to 4.5". For the front you can choose one of these:
1) As already stated you can find a 73-76 A-body donor car and swap the the spindles, UCAs, rotors and calipers onto your car.
2) Buy a set of wheel adapters, about 40 dollars from Summit Racing. I highly recommend against this but it is an option.
3) Buy a set of 67 Mustang rotors and have a machine shop rework them to work with your existing spindles and calipers. There`s a thread here on FABO outlining this mod.

The best method for a permanent change to 4.5" bc is to find a 73-76 donor car.

For the rear you can send your axles and drums and have them redrilled or as mentioned buy new axles and just have the drums redrilled. Another facet of this mod would be to seek out the later model backing plates and go with a 2.25" drum instead of the 1.75". Some people have gone a step further and found disc set-ups from late model Jeeps and modified them to work. Last, there are several aftermarket brake sets available if you want to spend the money.