So I see in my books that manual early C3 vettes got a different model Quadrajet carb from the automatics. Anyone know what the differences between the Quadrajet carbs were?

Steve

Some of the automatics used a vacuum line from the carb to the vacuum modulator on the trans. A few of these lines came from the carb, most from the intake manifold.
Some had a slight difference in calibration for idle quality in gear vs neutral (clutch disengaged). Ususally not there or barely if at all noticable.
Many had different linkage (or cable) on the side of the carb for the transmission kickdown linkage, that a stick does not need. This was the biggest and often only difference. Using the manual carb on the automatic often worked just fine. The other way around left off the kickdown linkage.

Ken Styer