The good news is that the top of the damper rods are the normal cup shape, meaning the valve/emulator/whatever will fit fine without an adapter.
Huggy's Speed Shop had some Harley springs in stock with a completely unknown past, they merely arrived in a container full of bits. £30 exchanged hands and they were mine, muhahaha! Harley spring and spacer on the left, BMW spring and spacer on the right..
Use the same trick to squeeze the cap back in the top and install the horrible clip ring thing.
So, there you have it - if you try this, let me know how you got on and what oil/springs/preload/valve preload you went with!