First some history I purchase this 55 fairlane over a year ago/the previously ower had a aftermarket power steering rack and GM pump installed/for the most part it works fine except  it is twitchy and darts to easy/I found a tech tip that says if you have a mustang II rack with a early GM pump replacing the 3gpm valve with a 2gpm flow valve will  take care of problem/my problem is how can I tell if this is a mustang rack and a early GM pump/any help would be appreciated