kevlar49, it is common practice in my area of the world (mid-USA) and class of work (Shell & Tube HX) to assign this material to curve B.
It is clear that if FG & N it is a curve B material, per note (b)(2). It is not so clear that any particular piece of plate is FG & N however. I don't have SA-387 handy at the moment to see if grain size is specified, however I believe it allows normalization.
Most often, the customer specifies -20 MDMT or lower so you impact test all of it anyway.
Regards,
Mike