u/Imaginary-Sock-1965

Looking to repair and restore an old plastic bumper from the 80s. It has no visible markings of what type of plastic it is.

The bumper has some holes drilled in it which I would like to fill and the corners which bolt to the fenders are also a bit wavy and the holes seem to be ovaled and thinned out quite a bit. Fortunately no cracks.

How can I fill and straighten these areas to ensure a lasting repair?

I was thinking to heat gun and flatten the wavy corners areas then bonding a 1/8 piece of AL under each so the screws don't keep digging into and compromising/thinning the bumper. Any thoughts on this or better repair ideas?