I can't claim this as my own but the idea is brilliant. Here is a cheap (free) and simple fix for sagging bumpers on cars with rubber mounts. And as a bonus, the bumper won't stick out so far.
Remove the bumper. Remove the rubber mount assemblies from the bumper. Now re-attach the mount assemblies to the car without the bumper. This will be your template. Stick a pencil through the holes in the mounts where they were attached to the bumper and mark the frame of the car. There will be two holes per rubber mount. Remove the rubber mounts from the car frame. Now drill half inch holes at all four marks.
From the car, remove the center pin that that goes into the backside of the bumper. Using a hack saw, cut off one inch of the front side of the pin. File the edge smooth. Fit the pin into the bumper to make sure it goes into the bumper hole all the way. On my car I had to file some material off the side of the pin. There was as small ridge that would not allow the pin to go in any further than it had previously. Reinstall the pin loosely to allow play.
Now simply reinstall the bumper using the four studs that were previously used for mounting the rubber assemblies. Tighten the pin and all four mounting bolts.
You now have a bumper one inch closer to the car and no bumper sag. The fit is the same as in the early cars that had no rubber mounts with no bumper sag. Here is how the finished product looks.
As a note: some may ask if removing the rubber mounts has any effect on shuttle shake or other vibration. Whilst I have not drive the care in every possible condition, so far I have noticed no difference. The weights on my car were removed years ago.