Martin
As I recall, taping steel cranks from 14mm to 9/16 was not too hard. Use sharp tools and the correct lubricant. Don't just use WD-40 or such.
Don't want to cause an up-roar, but you could also replace the crank with a semi-modern alloy crank. I see them on eBay quite often, some French Tange cups and a BB axle shouldn't be too hard to find either.
You could justify that as saving the original for the future.
Have fun
Brad Luecke
Columbia MO