According to this ebay ad, the turbo heat shields were originally to be made in polished aluminum.
Description from the ad, "I have acquired a small supply of these GNX TURBO COVERS from a machine shop in Michigan which was to hand make these covers for (ASC) and the GNX PROJECT.
The original specifications called for the covers to be hand made out of aluminum to dissipate heat off the turbo, but the covers got too costly and the GNX ended up receiving a steel silver painted cover instead.
There are over 10 hours just in polishing this cover by hand not to mention the amount of time invested in this cover being hand made!"
Ebay item # 200370896393