An ISO crank will sit farther out on a JIS spindle. This not only creates chanline issues, but can result in a damaged crank.

The simplest way by far is to buy French cups and a 118 mm spindle and use a vintage French crank. All of the old French doubles use that length.

Here's one that I converted to cotterless. I used Sugino cups and a Sugino ISO spindle marked MW-68.



I used the cottered crank on my beater Jeunet.



This one has an ISO cartidge BB made by Edco of Swizerland. Velo Orange used to sell them. I had to use it because I was unable to find the correct spindle for the triple.



I used Stronglight cups and a 118 mm Stronglight spindle on this one. I see them on eBay all the time.