Hi all - my first post.

I have a 74 LeSabre 455-4 ​​​​​in super excellent shape with 6100 original miles and always garage kept - photos below. I'm still cleaning it up from 50 years of storage, however the rear bumper filler has completely disintegrated over the years. I've got the bumper off and I'm looking for any guidance and any suggestions you may on how to replace these parts. Do I just line up the new parts with the top edge and drill small holes in the fiberglass where needed? I understand the replacement parts are now fiberglass in lieu of plastic. I'm pretty good with mechanical things, doing body work and painting, but I've never worked with fiberglass . Please email comments/suggestions to VAI@infowest.com.

Thanks / Ray