Anyway the Sachs ARIS freewheels need a Shimano (compatible) freewheel remover not a cassette tool.
I have been out to the garage and photographed both sides of a 501 rear hub. To complete the story I have also photographed one of my earlier hubs (just to prove myself wrong; there are bearing retainers - washers in Mavicspeak on that very useful PDF - on both sides in the earlier hub!
). To avoid confusion I will just put up the 501 rear hub now (I also have the front!)
Looking at the hub and the pdf it looks as if it ought to be possible to extract the axle and the freewheelside bearing just by unscrewing the "brake nut" that you can see on the non-freewheelside and tapping through. I have not done this, I don't know that it's doable but it looks like it should be. You're still stuck on the other side with the bearing retainer to be unscrewed but it may give a clue about the state of the hub.
I am still surprised that the bearings should seize, it's unusual on one of these hubs, they usually last for ever and a day!