I would imagine he set everything up with the timing set "dot to dot" and saw that it needed to be advanced. Since he was using a 9 keyway timing set he simply moved the bottom sprocket, lined it up again at "dot to dot" and got lazy and didn't set everything back up to re-check his work. Each time you remove the bottom sprocket to check things the degree wheel comes off and you have to find TDC again, set up the pointer, etc.
Matters not and you are correct, take NOTHING for granted and check and re-check these things rather than just blame the carb guy when your $13,000 455 build doesn't make enough power in a later T/A to outrun a Dodge Neon with a couple of plug wires pulled off of it!......LOL
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73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile),
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