I refinished the valve covers on both my M103's; one the hard way by sanding it, and the second using paint stripper.

Paint stripper works fantastic. Use a paint brush and goop it on thick, cover the whole thing with a plastic bag for about 1/2 hour and wipe the paint off. Use a wire brush to get in the crevices. Another advantage of paint stripper is that you dont have all the sanding dust infiltrating to the inside of the cover where it can cause problems.

I used regular old Rustoleum gloss enamel (enamel is more flexible than lacquer) and it has held up for three years now. One thing to note is that the original paint is put on very thick, presumably to cover the flaws and roughness of the cover. It may not be possible to get the same thick cover of paint but the new shiny finish is well work it.