I have seen the AC line issue vary.. all the lines are natural, except the line where it goes past the corner of the radiator, into the dryer, and every one of the "tall style" driers I have seen is black. This is in fact an NOS one, and of course we don't base everything on that.
Now, I have in fact seen natural alum driers, and natural lines, but only on the cars that have the later style short dryer. I have seen both on 70 cars, but the parts book indicates the long skinny one for a 70. It is also what was on the car.