I am painting my '68 SS396 and am curious about the proper way to handle the lower black portion of the body where it blends into the door jamb. Concerning both the doors and the jamb, what should be black and what should be body color?

Thanks

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1968 Chevelle SS396 - Yellow 4 speed, air, factory Buick interior
1998 Camaro Z28 - 6 speed
1999 Nissan Maxima SE - 5 speed
2000 Passat Wagon - 5 speed tip