I did it on my '76. I think it was worth it.
I found the front bumpers in good shape to be much harder to locate than the rear ones. Mine isn't perfect, but its better than most, and most people don't notice.
After you pull the bumpers and bumper shocks, you have to remove the tabs on the sides where the ends of the rubber cover used to hook. Then you fill the big holes that the shocks used to go through. Also, the thin metal tab that runs along the front edge of the trunk openning isn't needed anymore either. I is supposed to hold the top edge of the rubber cover down and in place. I think it was spot welded inplace and can be removed by drilling the spot welds out.
Finally, you drill new holes for the dogbone bumper brackets. I found this to be the trickiest part, because there isn't much room left and right for the bumper to sit off center, muchless look right.
On the original cars, there were L brackets welded in to reinforce the bumper mount to the side rail of the unit body. These are in the wheel well. I did not put anything in there, so my bumper and front panel would probably cave in an accident before the side rail. Maybe someday I'll have something welded in, I don't know. It's easy enough to do when ever I get the motivation.
In the back, you'll also need new license plate lights- the early ones are different. Also, there's a steel tab from the body, directly above the license plate, that the center stud from the rubber cover goes through.... another tricky part, getting it the right height and centered....
Good luck!
Jim
Some pictures- the back is a similar process.
Click to view attachmentstarted with this
Click to view attachmentbig shock holes to be filled....
Click to view attachmentshock holes filled, attachment holes drilled, everything primed
Click to view attachmentfuzzy pic, but the tab is there below the lock hole
Click to view attachmenttoday! TA DA!