Seems like a couple of .50’s sticking out either side would be pretty good too. Maybe a minigun someplace. :-)
On another topic, I’d really like to see the Coast Guard pick up some of these. Seems like an ideal long range SAR platform. Can cover a lot of territory in a hurry and carry a lot of stuff out, and people back.
Gun placement is tricky on this bird. In the “airplane” configuration the props swing very low. The gun placement would need to be as low as possible, meaning something in the belly or chin. But since the there’s little clearance on the belly when on the ground, a gun may need to retract when landing.
A retracting turret is going to be expensive, complex, and take up a third of the cabin.