Valve Covers:
I have never seen these valve covers used by anyone else.
I can't remember where I bought them in the dim past when I started my Speedster build.
I had to tap the holes in the heads where the original valve cover retainers hooked in. A kind of eye bolt fastens there. These extend between a couple of lugs on the ends of the cover.
Unlike the typical aluminum covers, there is no bolt passing through the cover.
There is a silicone o-ring in a groove that seals against the head.