a) Henson never thought about retirement. In fact, he was making/had been making a documentary film about the indigenous people of Chile when he died.
b) The couple described how they were eating/had been eating in the dining room.
c) The couple described how they were eating/had been eating in the dining room when the explosion destroyed the hotel.
d) She was breathing hard as if she had been running/had run.
Are all these sentences possible? Are they grammatically correct? Or are there any differences in the meaning?