About that Bell Model 17 suggestion. As lark has noted, the Model 17 attack bomber was to be a fairly straightforward Airacuda derivative with tractor engines (Lycomings, in contrast with the Model 9's tractor Allisons). So, we would expect to see the YFM-1's narrow, oval-section fuselage.
Instead, that l'Ala d'Italia photo shows an aircraft with a circular-section fuselage (or close to it). Perhaps this 'cannon fighter' was more closely related to the Bell Model 10 attack aircraft?