make your own open top valve cover and set after running temp for best results and to keep oil from draining down your block and headers lol! heres an old 6 cyl valve cover opened for this exact reason.
That's a pic of a Holden 6 cylinder with an XE/XF Falcon Weber carby on it...and roller rockers too, by the looks of it....possibly, Yella Terra Street Roller Rockers.