The Intermotor parts catalogue is located at
http://www.intermotorimport.com/Online+Catalog-eCatalog/Content.aspxGo to the 'Text Search' option and start typing 'Lancia...' and you should see a list of models it holds. Pick the 'latest' Fulvia model the database holds (1969) and then in the 'Major Systems' drop down chose 'Ignition'. You should then have relevant information which comes up as part number 'DR-2239'.
Now I realise this will be an S1 and you have an S2 so someone better informed than me will have to tell you if Marelli did any distributor changes with the model change.
Alternatively I believe the Bosch part number you're after is 1237013835.