Today, while browsing and updating my archive, I found some condensed info from the instruction manual of the Alfa Romeo Monsone.
What I didn't notice before (or maybe I did but I coudln't remember) is that the engine must be run on gasoline with 0.12% of TEL, which is also called '90 ottani tipo B4'
(90 octanes type B4). It's interesting to note that Alfa is using the same gasoline designation employed by the Germans in this document but they give a higher rating (90 vs 87) possibly because they rate gasoline using an average instead of the lean mixture value?
Other Italian airplane engines of the period either used gasoline with 0.08% of TEL (87 octane nominal) or, as I mentioned before, gasoline mixed with benzene and alcohol to obtain a similar effect.