Hi
I am not a D1.1 expert, but seeing as you have not received an answer yet, I will give you my interpretation of this. (Assuming that D1.1 is the applicable code for your job.)
D1.1 requires that the entire crack is removed, along with 2" of sound metal on either end of the crack. From your description, your crack lies through the entire thickness of the part. If this is so, then the additional 2" are obviously not applicable. (How do you grind and weld 2" of air?)
I really do not think that the intention of this paragraph is to require you to grind 2" in thickness.
Hope this helps.
Regards
Niekie Jooste
Fabristruct Solutions