8.8 on a 03 F150? I am pretty sure in 99 they all got 9 3/4's. Maybe the 2wd's still have the 8.8's. And i think the spring pads are different widths. The drum brakes are different too. I would try to get one from your generation, be so much easier.
the new 9.25 are used behind the 5.4L motor or other special packages. as for the rear end of a 03' fitting under a bronco...i dont know but what i do know is the bolt pattern for the wheels are different. also the spring perches might be in different places and they are for 2.5" wide springs.