I used a 17' length of line, including what was needed to do the eye splice. 5/16" is norm but I switched to 1/4". Just about any double braid line like NE Sta Set or Samson Yacht Braid will do.
When you mention "cable and rope" my 1980 has rope (line) only, no cable (wire). There is a D shackle attaching the line to the CB.
You can get the pendant and shackle from D & R Marine and know it is made up right.
Also, you don't want to use just any old shackle. The clevis pin cannot be longer than 20mm or it will jam in the CB trunk.