John, I haven't looked at the links Rodd posted, but just want to say that yes, you have to take the whole dash apart and it's a big job. Allow a few weeks if you're doing it on weekends, and while you're in there, fix everything you can think of 'cause you don't want to do it twice. Which you may have to do anyway, but the second time is easier. Now is the time to do it, before good driving weather comes back.
One tip: test run the blower motor on the bench for 5-10 minutes on both speeds. I didn't, and after reassembling everything the blower motor started squealling. That's why I took it all apart again. Better to find that on the bench.
Good luck, it's sort of a fun project...
George Davis
'69 280 SL Euro manual