I can safely report that it is possible to convert the old firing pin to the new bolt. Put the pin in a drill and used fine sandpaper and files to reduce the diameter of the pin. Then used a belt sander to remove the edges of the stop. Took about half an hour to reduce the diameter and 1 minute to remove the edges.

Have now discovered another problem. Spring in the Swissicon Vetterli is a home made replacement. Apparently the Italianicon and Swiss springs are the same. Now off on a search for a new spring.