The "modern design" would be the conductor itself. Resistor core wires used to have an enclosed column of carbon material in them. Later versions in the '70s and forward used some internal fabric stranding to take some of the "fragile" out of them as they were handled, but the conductor became "carbon impregnated". Still later versions used conductive neoprene with the fabric core for strength. All of these might fall into the "1000 ohms/ft" range for resistance.
In the early 1970s, a new conductor came out, I first saw it in a Holley catalog back then and later found some built by Sorensen Ignition under the trade name of "MonoMag". It was the monel wire that was wound spirally around the center fabric core. Metal "wire" that would not degrade radio reception. Seems like it was 100 ohms/ft. That same conductor is still around today. I bought a BorgWarner wireset in the later 1970s for my '77 Camaro. It looked just like the OEM GM wires except the plug boots were about twice the size--same color as the orig wires too. By that time, I'd put them on several Chryslers (and the Sorensens that came before them) and durability was good. Plus the piece of mind that I would not have to worry about handling them gently as they aged, if it came to that.
Chrysler had several different color combinations of wires on their engines (I recall more about the B/RB engines than A-blocks, though). Many wire sets were completely black. Later ones started using orange silicone boots in the early 1970s when underhood heat started to be an issue. The first electronic ignition cars usually had orange silicone plug boots and insulators, with black distributor boots. I also recall checking a plug wire on a new '72 or '73 Chrysler at the dealership and it was the spiral wire conductor (which surprised me, but it didn't either), but my parents '72 Chrysler had normal conductor wires on it. Also, all of the distributor-end boots were the smooth "tear drop" shape instead of the squared-off ones like many aftermarket wire sets use. Of course, it's not hard to change those boots from one wire to another, as long as they're in good shape.
When I checked the BorgWarner website, I discovered that their spiral-wound wire sets (which previously were "Cool Wire II" nomenclatured) are now "Select". I have not checked them to see what they look like as the last versions I bought were Cool Wire IIs. Other makers also have the spiral-wound core conductors too, but their authenticity in the cosmetics department might not be what is needed in some cases. Many auto supply chains carry the Select wires and the pricing is not much different from "normal" resistance conductor wire sets.
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