Hi Calif Girl!
How's your car coming along?
Well, reflective stripes were not used originally on the GT/CS. Non-reflective stripes only came in black, white, red, and medium blue. Gold was not an original GT/CS stripe color.
Reflective stripes became a standard item for the 1969 Mach 1, and Shelby (as well as the Torino, etc..)
If you wish to have added safety, then go for it. It will lose points if you're doing shows, tho'.
Reflective stripes and other vinyl items usually cost 60-90% more than non-reflective.
Just as an FYI.
Paul N.