The one time I removed the headliner from a 240, I was gutting the car and had a LOT of time. I figured I would take the headliner for giggles. It was a real ballet, and that was after I had removed:

front and rear seats

steering wheel

the front doors

I'm guessing you're working on a four door. I would remove both front seats, and the front passenger door. This should allow you to drop the passenger side of the headliner and line it up to pull the front end of it through the passenger side doorframe, pulling it towards the front of the car. You MIGHT be able to do this without removing the driver's seat- but you'd need to fully recline it.

Seat removal is pretty straightforward. The door is a little more involved, but only because you need to disconnect the wiring for speakers and door locks (and maybe power windows). If you remove the door, remove the bolts from the hinge to the frame, not the hinge to the door. Much easier to reinstall the door that way.

Good luck-