Hey Andy. This old Bronco is pretty weathered, but I believe that the vinyl is actually gloss. But, the vinyl of 1977 wasn't as glossy as the new high performance Cast vinyls that are now available. I think that is why the new vinyls look a little different from the original which was probably somewhere between present day gloss and satin. The original vinyl was also thicker than the new 2mil material (the original was probably about 4-5mil).
In conclusion, I believe that I would use "Satin" if black was the stripe color and gloss if white was the stripe color. Does this make any sense?!?!
I look at the pictures, and the old vinyl does have some shine ;Like on the front fenders where the fading paint the rust stained water hasn't "chalked" on the vinyl. Maybe gloss is the way to go. I remember several years ago installing the rally stripe on a concourse restored Mustang and the owner had found NOS stripes (which believe it or not were in great condition; the transfer paper was hard to remove), and they were low gloss black vinyl. Maybe about the same gloss as a slick paper printed black like a magazine would be. (Hard to describe the sheen).