The distributor rotating is the vacuum advance working. Note the distributor's position when the engine is off (no vacuum). Then start the engine and let it idle. The distributor should move CCW (advancing the timing) because idle vacuum is typically around 18 to 20 inches of mercury. Then rapidly open the throttle for just a second. You should see the distributor rotate CW because the vacuum drops, then go back CCW when you let go of the throttle.

'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.