bolt-up valve covers have proved to be nothing but a pain in the a$$ in my experience. they rarely seal as well as a good stock cover, ive seen them crack around the bolt holes when torqued up to spec, and i also dont like the idea of putting extra stress on the rocker studs.
maybe oliver has different reasons, but those are mine!
a stock cover with an elring gasket and a light smear of grease both sides, new bail clip and a welded vent tube are all you ever need .. finned ally covers wont provide much extra cooling if you ask me as heat from the head wont pass through the gasket too readily.