I have just added Kadees to a Vitrains Class 37. As you say it is difficult. The solution in the photo is neat. My alternative was to remove the buffer stops temporarily, remove the coupling mechanism (so I can refit it if I wish). Then just behind the headstock I plastic welded a small bit of plastic to have a base to fit the Kadee to. I used a #33. Then refit the buffer stops. This method means that simply with a scalpel I can prise off the Kadee and refit the original mechanism if I wish. However it does not look as neat as the alternative above but I wonder how the Kadee will react to a tighter radius curve since the bogie can push the coupling mechanism into which the Kadee is fitted. My solution has a restriction on what radius curve it can take in that the Kadee is fixed - it will just about do second radius I guess but I've not tested it that tightly.
