climberman...I collect a lot of aluminum valve covers.
The early 265 and 283 heads have 4 offset holes (two holes are closer together than the other two), In late 1958 or early 1959, the covers changed so the holes were straight across from each other (equally spaced).
You don't need holes in the valve covers if you have it as you say.
Do you have a type or style of valve cover you want in mind?