The Quest cone is for the T35 (35mm) tube, which would be closer to the ST-13, but wouldn't fit anyway.
IIRC, the cone on the Centuri Nike Smoke that I had in the late '70s was blow-molded. I never finished it - screwed up trying to get the correct taper on the fins. I don't have the cone any more, but I don't remember what became of it.