You've actually asked two questions.
The "Arning/Shelby drop" does not require any modification of the arm or ball joint. The 'drop' is a 1" relocation of the upper arm, and does not produce bind in the ball joint. If you go more than 1", you need a negative wedge kit. Of course, more than 1" will give you geometry changes that will be a problem on the street.
If you are looking for correct 4-bolt 67-69 upper arms, Glazier Nolan lists them in their catalog. IIRC, they are considerably more expensive than the 3-bolt replacement style. The 3-bolt is actually just the stock 70-73 type. If you use them, you should also use the 70-73 rebound bumper.