| Some models have long subtle straight lines that can be difficult to maintain or restore. Two examples of these are 68-70 Charger and Super Bee side belt bodyline.
The way I do this is to block sand from one side down to the line not being too concerned about going past it, just maintaining the correct contour.
Next, using a long metal ruler, I draw a pencil line where the body line belongs.
On a Charger, note that it is actually a vee; not a straight line the whole length.
Last, I block the other side being careful to sand right up to the pencil line, but not past it.
After finished and the line(s) are perfect, I do a light hand scuffing along the bodyline to soften it slightly until it matches the factory crispness.