Mine are all numbers matching too....the numbers match something else! Seriously, this is a super hot and ambiguous topic, depending on make, model, and group. I'm one of those guys who has been driving his GTOs as daily vehicles for over 3 and a half decades (less so now, though!), and during that time, master cylinders, water pumps, and alternators got replaced as needed in order to keep the cars on the road. Nobody really worried about water pump and master cylinder casting numbers 30 years ago....and the thought of sending out a pump or part to be restored on a car you needed to drive 50 miles to work the next day was not an option. I take pride that neither of my Pontiacs has been off the road since they left the factory. Registered and insured and driven every year for the past 50 + years. Not restored, just repaired ans needed and maintained. My '67 has the born with everything, except the trans. With my '65, the only numbers matching part in the drivetrain is the Muncie 4 speed. No big deal, IMO, on cars that have been my constant transportation from the age of 22 to my current age, 57, and still going strong! My hat is off to anybody who drives their GTO's and collectible Pontiacs as cars, because that's what they are.