I think we're over complicating things here. Campy shifters of that era used a slightly smaller barrel end on the cable. If you just buy a regular cable these days it'll likely have the larger Shimano barrel size, and then you have to file it. Look for Campy compatible cables and you'll be fine.

An example: https://www.ebay.com/itm/22391471451...3ABFBMpuP11Yth