They are Blue Thunder covers; cast aluminum; and a little unusual but worth the extra effort to obtain. I also have 4 unvented billet caps with o-ring seals. The caps come either vented or unvented, and are threaded. Two of my caps will be connected to an evac system when I'm done. The covers are internally baffled as well. Make sure you get the hardware (bolts, washers, and ask for SPARES!). The fasteners they use are long allen key bolts and replacing them is a real pain should you ever need to. Most standard breathers, etc do NOT fit the threaded breather cap holes. You'll have to do your own drill/tap job or order the caps already threaded...or have the company that provides the valve covers provide the breathers and fit them up for you in advance; it'll save the headache.
www.enginesystems.com is my preferred blue thunder dealer.
Byron