Did the factory paint the body color to the edge/lip of the rocker panel where it meets the underneath side of the floor that is painted black? Or did the black continue beyond the lip towards the rocker panel molding? I'm guessing that the factory just fanned the color into the black underside. In other words, where did the body color stop.
The pinch welded painted so much so overspray would hit the trans tunnel,....to make it correct,..you paint the floor black then with no disregard to the black spray the pich weld body color however much goes on the black is what it is
And half the time, that "cove" up under there between the outer rocker skin and pinch weld are not even covered with paint.
See attached pics of a 1970 Cornet Gold Buick GS 455 I did recently restored showing correct underbelly overspray.