How do you adjust timing on a 273?

The rotor turns clockwise looking down on it. To advance, rotate distributor counter clockwise. The rotor turns once, for two engine revolutions, so distributor degrees times 2, is crank degrees. Make small changes, verify with timing light. For stock base timing, this is often done at correct idle speed, with vacuum advance disconnected and plugged at carb. Consult service manual for procedure, and values. Many advance timing more, and recurve distributor.