Peter,
Where do you live?
For the last few years I have used Pitstart Garage which is in Park Royal, North West London (NW10).
They rent out their facilities so you can rent a 4 post lift by the hour. Not cheap, £30 per hour, but it includes the use of any of their tools etc you may require.
I normally put my GT6 on one of their lifts each year so I can have a really good look underneath, check the gearbox and diff oil levels, and change fluids.
I didn't use them when I changed the prop shaft because I was concerned I might get stuck or need something, and the hire charges are running. But I have found the other guys working there are happy to lend a hand. Most of them seem to be working on middle aged Mercs, which might say a lot about Mercs and their reliability, or about the people who live in NW10!
Happy to give you more information if you wish.
John