I did this once before...
I had the covers media blasted, milled, and I painted them with high temp silver paint. That was maybe three or four years ago and now paint is flaking off again. My indy said the covers are magnesium and that not much will stick to them. Powder coat should work better than anything and I would do that if I had to do it over again.
FYI, when you put it all together afterwards, use some Permatex anaerobic gasket sealer on the new gaskets. That will keep you from having leaking valver covers again within a couple of years.
Best of luck,
Robert
Robert Callaway
Dallas, TX
'94 530im 143k mi
'94 Land Cruiser FZJ-80 202k mi.
"If I could have back all the time and money I ever spent on cars.......I'd spend it all on cars."