What you need is a P/N 3923504 (see item #2 below), which was used on ALL 1968 cars and trucks with a 307 or 327 with 2bbl carb (except W/Powerglide), and all 1969 Nova V8 engines (except 396 or Powerglide). There's some conflicting information in the P&A's as to the color, so it was either brown or light blue, but the overall free length was 4.875 inches with 40 coils.
Note that it was replaced by P/N 492683 in December of 1981, but that part isn't the same design as the original 3923504.
Ed