Hearsay info. I have a 66 GTO with a 428, but I put it in. I once met an elderly Pontiac Dealership owner, I believe the dealership was in St. Paul. I visited his home and saw pictures of 60's stacked headlight cars, so I asked about them and told him what I had. He told me that he had GTO with the larger motor, factory installed. Now I cannot remember which year of car, or whether it wby Craig Anderson - Pontiac GTO Forum