I would leave the rear bumper, that is weight in the area where you want it....also to note, the back seat really doesn't weigh a lot, but if you are going all out go for it...just my 2 cents.
Edit: Removing the front bumper (with brackets) is about 33lbs off the nose, which is good. When your car gets faster this will be a very useful change (speaking from experience with my 67 Barracuda).
