Paint matching a 50-year-old car is not color matching a 50-year-old car. The color that went on the car in 1967 has been modified by UV exposure, by wax buildup, by oxidation, by every wash and polish since. The formula in the paint supplier's database will match fresh 1967 paint, not aged 1967 paint.

I use a spectrophotometer to read the actual current color off the car before I order any paint. Several passes on different panels that have seen different sun exposure. Average the readings, tweak the formula, shoot test panels, compare in different lighting conditions.

The goal isn't a car that looks freshly painted. The goal is a car where you can't see the join.