Jerry's right. He usually is. I just checked mine and it is connected to "ported vacuum" on my carb.
I started the engine and then pushed the vacuum advance linkage to "full vacuum" with my finger. The engine stalled as expected.
My timing is set to 7 degrees before top dead center at idle, which is 2 degrees more than the book calls for, but the engine seems to like it better. I set it "on the BB" which is 5 degrees before TDC with a timing light. Then I adjust the "octane selector" to where it seems to run best. That way it is easy to take it back to the factory (or anywhere else) setting without needing a timing light.
This was done on my GMC with a Carter YF carb and a '56 Chevy distributor. Chevys and GMCs used the same part number distributor in the late 50s, I don't know about early 50s. Your Chevy/Rochester mileage may.
'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.
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