I purchased valve cover adapters from SuperHart. They allow you to bolt true 427 style valve covers (both cast aluminum or stamped steel) to 351 heads. The adapter plates are thin (about 3/8") so they do not show but they are very strong. The design is very neat; SuperHart counter-sunks all screw holes to create a very flat surface for the gaskets to pervent
oil leaks. The machine work is top notch!
He also provides great instructions and advice from years of fitting all types of valve covers. The service is outstanding; I needed slightly longer screws and SuperHart machined the screw heads and sent them to me with a few days at no charge.
Strongly consider giving your business to SuperHart. I am a satisfied customer; no more, no personal interest. I really appreciate great workmanship and service.