The body should be lifted to replace the rear A/C pipe work, but I don't 'think' the body needs to be lifted to replace the rear AHC pipes, so there might be some confusion between A/C & AHC pipe work from your advice source, you may need to remove the fuel tank to get to the N/S AHC pipe, also can be a pig of a job to get to the top of the rear hydraulic rams, I have read that some have cut holes in the rear floor to get to the top of the rams, the prob is that Toyota assembled some of the parts on the chassis then put the body on top, so making access to some of the parts almost impossible.
I have thought about replacing my rear (as it seams to be the rear that corrode the worst) AHC pipes, so I have done some research, but have NOT actually done the job.
So my reply might be a load of old BS.
Whether my advice is good or bad, I wish you good luck.
P.S if you do the job, let us know (in detail & with pic's) how you got on.