You will likely have to remove the gearbox crossmember and support the gearbox from below with a screw jack or something to hold it in place. Use a piece of plywood or something to keep from bending the pan.

On my SDL, removing the carrier bearing was enough to get the driveshaft enough movement to get the front flex disc out of the way. Will take a bit of wiggling, but you should be able to do it without pulling the entire DS.

Since you're down there anyway, consider replacing BOTH flex discs. The rear one is pretty easy and if it's the same age as the front one, it probably isn't in much better shape.