What is the difference between the Q and R codes in the 69 Mach 1s? I know they are both 428, but does one code designate Shaker hood, etc.? Just curious, as I am thinking about buying a 428 Mach 1 but not sure if it is a Cobra Jet or what makes it a Cobra Jet, or if either of these codes designate the Shaker hood. THANKS!