You can tell if your bumpers are fiberglass if they are almost completely rigid.  Urethane flexes quite a bit, and Tru-Flex flexes noticeably.  Before  repainting, try buffing the existing paint, just in case it can be saved.    Professionals use a wheel that removes decals, including pinstripes.  If you don't want to invest in one, the safest method is your fingernail.  If you try to scrape, you risk scratching the paint.  You might have some luck with adhesive remover, but you will probably need to get most of the tape off first.    If your mags are chromed, 000 steel wool will clean them up, and any car wax will protect them.  If they are aluminum, there are many metal polishes on the market.  My personal favorite is from Dry Wash and Guard, but there was a recent posting on this forum that named several others that people liked.

Good Luck
Larry

If they are the stick on pinstripes, heat them a bit first and they come off much easier.

Might want to whoa up here.  There are no factory stripes on the '81 models unless you have a two-tone paint car.  If you have a two-tone, your tape stripes are probably original.  Although replacement tape stripe kits are available, you might want to think things through before pulliing off original stripes.