Could be the fiber timing gear. Could it be a "clack" rather than a "click"?
When the gear becomes loose on the knurled steel hub it works fairly well for
a while and the noise gradually gets worse and worse and then (if you're lucky)
it will occasionally slip, especially at high revs, and then stick in the right
place when the engine is back to idling speed. It's like you really wrap it
up and then like you turned off the key, but when you step on the clutch and
roll to a stop it's idling perfectly. Happened to me several times on a trip
in my 164 from Cherry Point to Daytona on US 17 around Charleston. Pretty
scary. About 2 weeks after we got back to Cherry Point it quit for good.
That was at a measly 120,000 miles if I remember right, about 1979.
Gotta put those steel gears in it one of these days!
--
George Downs Bartlesville, Heart of the USA!