Hi Phil,
Here is an old post but this is what I did with my engine and it worked great:
Valve cover sealing
I purchased the 5/16 thick cork gaskets from DSC and used the Right Stuff to attach them to each valve cover. I then bolted the valve covers to each other (with the gaskets sandwiched between them) overnight to keep alignment and compression on the gaskets while the Right Stuff set. The next day I used a light coat of grease between the cork and head and never had a leak.