These guys are all hitting home on this one. Many paints are no longer legal to buy/use (e.g. lead pigments or paints with tons of solvent).

Even if the paint "looks good" there has been "some" fading + every batch of paint (even back in 60's/70's) varied in color just a touch batch-to-batch.

Bottom line... it should be custom color matched. You can get test panels sprayed up (with an appropriate primer as close as possible to the original primer on the car) & blend several small batches to get the customer blend really, really close. Then, have someone who does custom paint work or an auto-restoration shop spray it, blending in the repair, as these guys have mentioned. That's the best you can do.