I confirm that the idler box should be removed to extract the arm. Because of its conical shape, a standard puller will just slip away from the arm and in fact Lancia had a special puller for this job. The same tool was used on the Flavia. Quite difficult to find nowadays: a picture can be seen at
http://lancia.co.za/article/Flavia/Flavia+Saloon+1.5/Tool+LANCIA/8062024.html. This does not seem the original tool that I got (a very long time ago) in my garage, but it will probably do the job. Andrea