Bumper replacement necessary on '91 Classic?

[Dan]

Over the weekend, someone backed into my '91 Classic in a parking lot.
As far as I can tell and (unless some internal impact-damping part was
damaged, which I will have to check) they just scraped and blackened
the bumper on the offside rear corner. The guy seems willing to pay for
any necessary repair rather than go through his insurance company. My
question is can one of these bumpers be refinished and repainted or do
they have to be replaced? And if the latter does anyone have a) an idea
how much they cost and b) a part number? Thanks

	Dan