Ha! See I didn't know the answer 3 years ago either. Here is what was said.
"When I was buying my six pack (all new parts) I saw that they only listed center carbs for an auto trans. I called Holley & was told the only difference on the replacement carb is the auto trans type has the arm for the kickdown linkage. Otherwise, they were identical. I specifically asked if jetting or anything like that was different & was told no. Don't know if this is the same for the originals or not."