Wolfgang mentioned up above that the original FF/CMC header is made of laminated fiberglass. Having modified several of them for myself and others, I’m not so sure.
I’ve cut into and drilled several of them and they don’t act like laminated fiberglass. They act a lot more like someone came up with a mold and poured runny Bondo into it and let it cure. None of them looked like they had much machining from the mold to the final, useable part (a nice way of saying that they were pretty “rough”). Usually, when you cut through laminated fiberglass the cut shows Frosty clear or amber/white. When you cut through the CMC header the cut might show solid white or blue or gray.
??????
Every one I worked with needed to be modified slightly for the windshield frame slot to actually fit the shape of the windshield(s) and no two seemed the same.
Not saying they are better or worse than anything else, just like a bunch of other CMC stuff - Just a little Weird.