Yes you can screw the black plastic bezel to the dash frame without the metal housing behind it.
Can I get rid of that metal peice completly and mount the gauges to the black plastic peice
I don't think you can mount the
original gauges to just the plastic bezel since you need the metal housing to ground to the frame.And you have the
Clear plastic bezel that clips to the metal housing to protect the original gauges.
Maybe some custom gauges.
Good Luck