I'm wondering if the aluminum bumpers on my 78 hatchback came from the factory with some kind of coating on them or if it is the same aluminum all through the bumper.

Somebody that owned this car before me must have never gotten used to how far the bumpers stick out on these cars and hit everything.  There are scratches and scrapes everywhere.  Can I just sand the damage out using 220 sandpaper and work my way up to polish or would I be removing some important surface layer?

The bumpers have an anodized coating on them. Mine  were pitted with white spots all over . I sanded them with a power vibrating sander starting with 100 grit, finishing with 1200. I also used oven spray to help in the process, as that eats up some of the anodizing.Afte r that use a good aluminum polish and they will shime like chrome. 

This stuff..

http://www.sharkhide.com/

what about the trim around the drip railings on a '78?  Mine has some kind of ruined coating on them, but the door and wheelwell trim is good.

If I remember correctly the drip railing trim is metallic coated plastic and crumbles to pieces if you attempt to remove/repair it... on that note does anyone know of anything to replace it?

Early cars had stainless drip rail trim instead of plastic.