Originally Posted by
5vforest
Or even better, tap the Swiss BB shell out to ISO.
You can't. Swiss is 35 mm diameter and English/ISO is 34.8 mm so the hole is already too large. The OP could have the bb reamed and tapped to Italian threads (36 mm) which would open up a whole world of alternate bottom bracket models.
I agree that looking for a new suitable spindle and keeping the current cups is the cheapest solution.