First of all, according to Marco Giusti's Dictionary as a producer you was allowed to partecipate in a minority co-production only after being involved in a majority co-production. In the same way, you was allowed to participate in a majority co-production only after producing an entirely Italian movie.
For co-productions with majority participation, the requirements to get State contributions were:
a plot from Italian author
at least two out of three screenwriters
two-thirds of main actors
three-quarters of seondary players
three-quarters of other crew members
For minority participation, at least one screenwriter* and a few actors and crew
members (unspecified number).
* This explains why in the Italian version of Cemetery Without Crosses Dario Argento, in all probability responsible for the Italian dialogues, was credited as third screenwriter.
In Spain the requirements were slightly different but equally complicated.