Hi, Tom.
Rich's response there really sums it up, Anto is the resident authority on Kadees and there is also a wealth of info on other forums regarding fitting them to your stock.
Rich also describes fitting the Kadees to the underside of the coach as opposed to the bogie which is the norm with US/HO stock. This is also prototypical and the way the couplers themselves are designed to operate.
I initially tried this but found I had nothing but problems when traversing curves on the layout. I found through other forums that the majority of UK/OO modellers opt to fit them to the bogies so I tried this method and found my problems disappeared! Whether is was a problem with my fitting methods or the amount of tight curves on my layout I just don't know, but I had to go with what worked best for me.
You can see in the pic below that fitting them to the Lima MK3's was simply a matter of removing the tension-lock hook and attaching the Kadee no.5 directly to the top of the bogie. The coupler height gauge that Kadee supply is absolutley essential for the getting the coupler to sit at the correct height, and by pure fluke the Kadee happened to sit at just the right level.