I have both. I kept the 50 crank case tube tube with oil filler access and veneted valve cover as well as the 55 crankcase tube and vented valve cover with oil filler access cap.

What I want to do is use the 50 (old script) GMC valve cover but there is no way to fill. That's why I wondered about the standard small block V8 tube being used as a substitute for the road tube. Seems I would get filtering plus venting at the rockers as well as the cranckcase.