I have a 66 Coronet 500 which we just started taking to the track, it’s more of a street car. Before I took it out I ask the tech guy about seat belts and when I told him it would probably run in the 12s he said the stock seat belt would be fine. The first time I took it out it was in the mid 11s and I didn’t feel comfortable with the 50 year old lap belts. I ended up ordering 3 inch 5 point Simpson belts and as per their instructions the shoulder belts use the rear seat belt mounting points behind the driver and come out between the upper and lower seats. I thought mounting them that way would make the shoulder harness too low and too much of an angle, but it seems pretty good and is way better than just the stock lap belt.