I disconnected the drive-shaft at the rear 4 months ago when I towed my 1985 300D. I re-installed it at night in a parking lot. The left rear wheel was on a curb and the body jacked up on the right side. I put the rubber disk on the drive-shaft end (should have left it there while towing). I was able to pry the drive-shaft forward enough to barely slip it into the differential's yoke with only a little swearing. Seems having both rear wheels hanging would make it easier. Sounds like you have a new front disk installed (stiffer), so might be tougher.