Been looking at doing the same for my night train Roka. So done a bit of browsing on the us version of hdforums. Lot of the guys there recommended the arlen ness extension kit as it is 1/2 the price of the hd version. Here's a link to the kit. www.arlenness.com/p-1068-extension-kit-07-09-softail.aspx
This might help you also.
hdforums.com/forum/softail-models/368238-fxcwc-3-forward-control-extensions.html