Take off the Valve cover . . or, just put a sealed cap in the breather provision if the valve covers come with one . .
Racing engines generally don't have an "Oil Filler Cap" . . If you really race the car, you've got the valve covers off after every race weekend to run the valves and look for shavings, sparkles and other non oil particulate in the lower parts of the head . . As well as inspecting the oil in the pan and filter . .
Happy engine, happy wife . . .