I believe they are indeed called "valve cover drip rails". They help accumulate the oil that splashes on the top of your valve covers and then channel the oil to drip in specific places; notably on your rocker arms, instead of letting the oil run down the sides of the valve covers where it cannot help cool the rockers.

My '69 w/ a 350 2bbl did not have the drip rails, and my 400 w/ roller tip rockers and stock height chrome valve covers that I am rebulding now will also not use them.