A buddy of mine runs a 377 stroker in a late model Mustang with a hydraulic cam,he likes to adjust his valves with a warm engine running, so he took an old valve cover and cut a slot across the top of the cover about 2/3 the width of the top from end to end.....
Install on car and you can access the rockers arms from the top and keep 99% of the
oil in the motor, no mess, no smoke.....
Just get an old OEM Factory metal valve cover and make your own.......
David