I think Nick Hahn, in a DGJ article on Italian OU's, referred to that as a "proprietary" (might not be the word he used) Italian action. Quite a few Italian OU's built using that somewhat modified Kersten system.
If it's a Zoli, there should be a bow and arrow proofmark somewhere.
I've been looking for that bow and arrow and there is a smear of mark that might be on but my eyes are getting even weaker then my brain and as of yet have not brought to bear needed tools to read the bloody thing. The ksi 400 does indeed look more like an inspectors mark then one of a manufacturer and am a bit embarrassed at my not being able to discern the obvious answer. Thank God for a place we can go where, in the matter of firearms at least, wisdom regularly trumps ignorance.