Hi Export, I had a set of old NOS stripes for many years which I tried to apply lately and they did not turn out so well, during application they trapped air bubbles in numerous places which could not be removed, so sadly ended up destroying them. They where a hi quality 3M product but where from before 1988 as the 88 Olympic logo was on the backing paper. They where a matt black but did not match my painted hood striping which is a semi gloss finish that is supposed to be the correct color based on paint codes I have receive through different sources.
The matt black on that old kit is less shinny then the semi gloss paint, I guess not a big issue on the trunk stripe but placing the matt black 428 numbers on the hood in the gap between the painted stripes will definitely show the difference between them. I have been told that the striping kits do have a shelf life and should be used within a couple of years or so, but I can not confirm that. I am just going to have to order a new kit from a vendor and see what I get and for the 428 numbers if the color is not close to my painted hood strip I will have them custom made by a local vendor.