I suspect that it must be a kit part: it is cast, not machined, and has the letters "CFC" cast in on both sides. Also, the dark patina makes me wonder if it's magnesium.
The PO gave me no info on the parts on the bike, but he evidently used all the best stuff available back in the '70s. I just recently found out, via a classified ad, that my foot pegs and levers are John Tickle. The bike also has a Gremeca rear disc, Morris wheels, Gerex ign, and Webers, in addition to the Seeley chassis.