Just picked up an '80 Regal Limited, 3.8 for now and wondering how to replace the rear bumper filler?
http://www.gbodyparts.com/index.php?cPath=46_22_26&osCsid=068029662cb4aa3921c2b8408d4da00d G body parts has them, but be sure to call and make sure they are in stock before you give anyone your money.
I've never changed them on that early model of a Regal (only 84-85) but just had to remove the bumper then remove the fastners holding on the old fillers. I have only used the fiberglass replacements and found that they hold up the best to weather/sun and spilled gasoline on the back one. If by chance you use the fiberglass fillers and some of the holes don't align like you want, don't be afraid to enlongate the hole with a small round file.
Thanks! Just waiting on the seller to get the title and then I'll be hitting the catalogs. My buddy has a 72 Grandville 455 that he wants to donate to the Regal, that could be interesting.