Plating isn't like a paint or powder finish where there is a great difference in depth, sometimes we have to plate parts at work because powder takes up too much of the tolerance. Its more like anodizing where its a surface change rather than a finish.
Plating alumnium isn't as simple as steel but most places should still be able to do it, however I couldn't be sure of the cost, probably not be cheap as its a batch/mass process usually. To get a good finish it would be best to polish them flat too which in itself is a ball ache.
Zinc and gold/yellow could look quite good but also look abit crap, could help with heat reflection though!
You could just get the cover powder coated, as with a lot of other brackets etc.
Decent tap set should only be £20-30, I got mine from machine mart and use it quite regularly now, cleaning threads out anyway before a re-grease!