Ray,
just in front of the center support there are two hex sections on the driveshaft. These are used to adjust the length of the d/s, and also help with removal of the flex disk. Wrenches needed are something like 40 mm and 46 mm, but I can't swear to that. When loosened, the front shaft can be slid back a bit. I've also found it helpful to unbolt the center support so the d/s can be flexed a bit, too.
When you reassemble and have everthing hooked up, leave the d/s length adjuster loose, roll and bounce the car to settle things, then retighten the length adjuster. Make this final adjustment with the bottom plate in place and supporting the trans as normal.
Last, you don't want those flex disk bolts to come loose, or the d/s flange or trans flange or both will get mangled (ask me how I know). If you're replacing the disk you should have all new nuts and bolts; they should be torqued to spec. If not replacing the disk, you've got to make sure they won't come loose. The nuts may be all-metal lock nuts, but I've never really been sure of that. Good luck!
George Davis
'69 280 SL Euro manual