Builders of competition engines have been timing cam shafts for years. The most common ways are stepped keys or vernia sprockets. Make you drive so that it uses plate sprockets and drill a number of possible mounting holes. A dividing head is good if you have one. Then choose the appropriate point to secure the sprockets. If the torque isn't too high, you can get away with slotted holes. I must admit I like Larry's idea of variable idler sprockets. Not come across that before.
John
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