Defiant - sorry there's no pics of the breeches / feed.
Lancaster. The ammo for the rear turret was held halfway down the rear fuselage (for Cof G reasons I've been told...) and the belts travelled down a track to the turret. How they entered, I don't know. At Conningsby last week, we were told that the turret was held on by 4 bolts...
HTH