Difference between carbs?

[WiggyHD]

So, I pull the carb off of the 340 to rebuild it.  I write down the numbers, and it turns out the it is a '72 MT carb (6138 S), and the car is an automatic, so it should have a 6139 S carb.  What is the difference?  I will still track down the proper carb.  Just curious.  I'm thinking maybe there is an extra vacuum port?

Mark 

[Bullitt-]

The differences I've seen are minor although I've never had a 6138S in my hand.  The accelerator pump linkage sets up different but even that is an adjustment which could be made to specs for an automatic car. Some other measurements are different from manual to auto just follow the instructions for the auto. No vacuum ports are relative to auto tranny.

[WiggyHD]

Thanks!

Mark