As Smudge says, axle stands were enough. The yellow set are approximately 14 inches -note they are not extended, and located on the jacking pads on the sill. The red ones are a slightly shorter pair I have had for decades. These were used to support the trailing arms and hubs whilst working disconnected from the arms, and left overnight, with bungee cords used to tie up the exhaust too. I did mine over a week, as I was cleaning and painting the bottom with underseal. if you are planning on other jobs whilst changing the frame, think of other components, and any support they may need. In my case it was the trailing arms and exhaust.
Before
during the change (you can see the old subframe with arms lying below the car).
