Compared to the Saiga rifles, the primary dust cover on the shotgun receivers have a longer notch on side with the charging handle to allow for clearance of the ejected shells. The problem that I have seen with this is that the safety selector, when pushed upward to the "Safe" position, frequently travels well beyond the top of the receiver, only stopping after it begins to set underneath the dust cover. This can make it rather awkward and difficult to move the safety into the "Fire" position, even with a modified safety selector (like the Krebs Mark VI-S).
I am thinking that possibly