oil return holes in valve train valley

[jiw1]

hey guys,does anyone know what the size is of the return oil holes are in the valve train valley? the reason is,i have a 53 8rt low miles that has been setting for a while.i did start the engine for a few maybe a minute,it does start.turning the engine to do compression test noticed two cyl's did not have compression.pulled the heads off and found valves to be stuck open.removed intake manifold freed the valves and all moves find.there is a lot of crud in the valley and would like to plug the oil return holes so i can soak with atf and kerosene to clean it up without taking it all apart.any info is welcome.thank you,john