Are the measurements in the "Guide to Buick Gran Sports" by Steven L. Dove the best available. I know the stripes were all slightly different with overlaps, which I'm not doing, but are the books measurements what everyone else is using to lay them out by hand?
That is what I used. Still mine are not perfect. No one is going to question it as long as they are neat.
The stripes on my original paint '70 are so wavy the painters were either drunk, or there was one hell of an earthquake while the stencils were being applied. As long as you are close I'm sure you'll be within factory tolerances.