Attached are a few pictures of the stripes from an original, unrestored 03D build date '69 Pace Car. They show that the spoiler was on the car at the time the stripes were painted, and did not extend beyond the front edge of the spoiler. The '69 assembly manual, pp. 474 - 475, shows where the D80 stripes are to be painted on a car with the D80 rear spoiler.
The quality of the masking was not that good and allowed considerable stripe color overspray to “peak out” beyond the indicated boundaries. As we restore our cars, it difficult to intentionally be this sloppy.
Good luck with your project.