I cleaned up the welds using scotchbrite discs in a low rpm angle grinder and various shapes grinding bits to get in the tight spots, then I spent a few hours with plain oldfashioned sandpaper. The 2 large holes where the air from the scoop will escape I drilled with the largest drill I could find ( about an inch in diameter) and then machined out to the final size.

Last Thursday I went to pick up the wheels from Haan Wheels, where they had made one-off rims and spokes in stainless steel for my one-off halfdrum hubs. All the parts were nickel plated and I am very happy with the way they turned out.
More pics of my visit to Haan Wheels here

As a test I had a spare enginecover clear anodized, but it came back with an uneven grey finish, not very pretty. Oh well, it was worth a try...