From Mechanical Database

Tools & materials:
9 ft of aluminum strips, 1 in wide, 1 mm thick 3M scotchbrite pads Alum polish such as 3M, Mothers, and Meguiars etc. A drill or rotary buffer to polish the fender plates. Can be done by hand, but it far more difficult. A handsaw or Dremel at hand to finish and round the corners.

This do it yourself article describes one detailing option that might cost you as little as $10 and just a bit of patience and a few simple tools. Detailing the engine bay is not a common activity as it's usually lower on the priority list than exterior and performance.

Procedure

1. Measure the length of the fender mount rail and cut the strip to the desired length.
2. Mark on each strip the spots of the fender bolts, you can use a nail for this.
3. Drill the 3 bolt holes on each strip; make the holes a bit larger so you can adjust the location of the strips when you mount them.
4. Trim the ends of each strip to the desired shape, a ¼ circle looks ok.
5. Remove the fender bolts and test install each strip, if ok continue with the next step.

Polishing

1. Use some 400 fine grit sandpaper to remove all the scratches, wet sanding works best and faster.
2. Follow this with 600 then 800 grit.
3. When the surface is smooth you have 2 choices, polish to a mirror like surface or just leave a clean aluminum look.
4. If you want the alum look just use the scotchbrite pad to finish the surface, always move it in a straight line.
5. If you want a mirror like look use the aluminum polish either by hand or using a drill or Dremel.