Originally Posted by
John E
...your biggest challenge will be in finding either a spindle that lets you use your existing cups (it's mostly a matter of wall thickness)...
I have successfully used the 5SB spindle. They are kinda rare and expensive:
https://www.ebay.com/itm/305366039434
You can also use a Thread-less Bottom Bracket. They cost less then a new spindle and save ya a lot of fiddling.
Good Grief Charlie... How many of these cottered cranks, chains, and other bicycle Do Dads, have I given to our local knife maker? Just checked the garage. Nope, no cottered cranks there. Sorry...