Fixing a Sturmey Archer AW hub is on my list of things to try in the near future. You need one that was manufacture after 1962. You end up with a direct drive and a 25% reduction as well as a nuetral. From what I've read there is a lot of slop in the system that feels like a loose chain, but it's the insides of the hub moving around until eventually it breaks. There is a more refined conversion process where you fabricate a new clutch plate which tightens up the whole works so it feels more like the old ASC.

The last two or three ASC models I saw on eBay went for around $400. The shifters go for almost the same.