Just for S&G, I stopped by my local cycle boneyard today; the 75 CB750F I've been leeching parts off of was still there; kickstarter in good shape. Took it home and...
The Good News: The spline is the same as my CB500 and CB550's.
The Bad News: No way this sucka will work on a 500/550!
The clamp part of the arm mounts toward the front, and the 500/550 clutch housing is in the way. I even tried taking it apart, mounting it upside down, and/or reversing it. Nope. Ain't gonna work!
So...If I want to clear both my mufflers and my rearsets, I guess I'll have to find a CB550F kickstarter and try that...