What is the correct Q-jet code for the 1969 Camaro 350 automatic? Was it the same for the 255hp and 300hp? Was there any special about these carbs that make them different from later models?

The carb number (code?) should be #7029202, it was the same for 255 or 300 HP. The carb was made by two (2) sources - Rochester and Carter. The Rochester units have stamped numbers the Carter units have a round tag and say 'Mfd by Carter'.
Nothing special about any of them externally except for throttle lever differences and choke type. The other changes are inside and not easily seen.