Okay, I'll reply to myself since I just finished the job in case it could help anyone else out.
Not a bad job at all if you have enough jacks and stands. No need to drop the driveshaft, but it does help to take one nut off the rear safety strap under the shaft, loosen the wire connection to the differential at each of it's grommet support points. I supported the rear control arms and disconnected the shocks, sway bar links, and even the pivot bolt and dropped the springs, carefully!. Then support the differential in the center on a jack, remove the 4 bolts that attach the subframe, and gradually carefully lower the whole rear diff/subframe assembly about 4 inches. After removing the bushing supports on the sway, it will snake out and the new one in.
Test drive of the E500 rear bar in my E420 comes tomorrow.
(Oh man, this car is sooooo fast.)