Hi,
I have one just like it. Mine came from a Mac Road Runner trimmer. It is 21cc. To remove the clutch, clamp the clutch guide in a vise, jam the flywheel with a screw driver through the flywheel fins and against the shroud. Turn the block. It is a 8x1.25mm stud at both ends. The timing is very conservative at: Intake 110 degrees duration,exhust 120 degrees duration, transfer 90 degrees duration. It looks like it was made by Koiritz for McCulloch. The ring is floating. Very heavy fly flywheel at about 12oz. Good quality.

Dave