I would say on anything other than a serious performance car, a BBK at the rear is unnecessary. I would only do the front, if anything. Though really, unless you are tracking the car, a BBK in itself is overkill. It just looks cooler is all. If you want to make use of the braking power you need wider wheels/tires.
Btw even with that swap you'll need the motor bored and stroked to make 300 whp.