First I will say that I agree with custom Jim that sectioning the bumper along with tucking them is the best way to go. Unfortunatlly that goes beyond my skills. The way I did mine is not the best way, but it was easy and required little work.
I did this about 9 years ago so some of what I did is a little fuzzy, but basically what I did was collapse the bumper shocks by drilling a hole in them to release the pressure, then remounted the bumper shocks back on the frame about two inches toward the rear of the car. This will require you to drill a couple new holes in the frame for the new location of the bumper shocks.
The stock bumper filler is discarded, and the chrome trim under the grille becomes the new bumper filler. I would have trimed the rubber corner fillers that mount under the fender extensions to fit, but mine were wasted.
A better way to go would be to fabricate some new, lighter bumper brackets, but I do not possess those skills. I did however cut away most of the inner shell of the bumper to save weight.
I can also attest to the durability of the new set up. With out going into to much detail, the front of my 05 Silverado got acquainted with the front of the 74 in the driveway over the winter with these results...
I destroyed the grille, but the bumper didn't move.
John.