The most prominenet example I can think of is PLAY MOTEL (1979), which contains a fair share of hardcore footage.
And GIALLO A VENEZIA (1979) includes some brief hardcore footage of a guy masturbating at a porn cinema. However, I suspect that a version with more hard scenes existed at some point because several sex scenes are shot in a way that would easily allow for inserts.
DOUBLE FACE (1969) is said to have been released in France in 1976 in a re-edited hardcore version called CHALEUR ET JOUISSANCE. The added hardcore footage is said to feature Alice Arno. I can't vouch for this, though, since I've never seen this version.
And I think I remember reading that there's a hardcore version of the semi-giallo THE BLOODSUCKER LEADS THE DANCE (1975).