The two PSA L-1011 with the lower deck seating in what would be the fwd bag hold did indeed have an armored skin up front in the event of a belly landing. When Worldways of Canada bought them they were brought to Eastern Air Lines Contract Maintenance where we removed the lower deck seating. In order to lighten things we also took close to 2000-lbs of belly armor off. That was quite a penalty for seating downstairs.
The L-1011 galley "lifts" were initially very troublesome proving again the old axiom, "Don't buy the A Model of anything!" In the event of both lifts being jammed down, you could go out through their ceiling to the main deck. If both were jammed up however the lower galley occupants were trapped. Pressure sensors on their top prevented them from coming up if anything was on top of them. Never saw the DC-10 system so can't comment.