Sorry I did not get back to this site sooner!
Anyways, I looked at my carb very well and it looks to me that even though it is the correct carb, I feel that they must have just cut that arm you mention off ..
It is a clean and smooth cut if that is how they did it?
I have several spare thermoquads for both 72' 340 manual and also the auto trans, And they all have the arm that you speak of...

So I think they cut it off !
Just FYI.
Grant Eaton 386-561-1181

Owner of Original collector and restored original mopars from Mr Norms Grand Spaulding Dodge.