Pre-RVSM days I remember hand flying a B737-200 from Madrid to Gatwick as both autopilots were u/s.
Me and my oppo took turns for about 10 minutes at a time.
It was tedious! At one point I remember one of the hosties being in the flight deck and getting another of her colleagues to walk up and down the cabin with a catering trolley. She was amazed at the affect and the input required to maintain altitude.
It probably wasn't the comfiest of flights for our passengers!