Thanks ... I was actually thinking about this this morning! I should probably just buy a set of Bachmann couplers. As you say, I should easily be able to swop the metal ones on my Hornby wagons with the Bachmann ones. But I could still do with a few more wagon/vans anyway, so I may as well by Bachmann ones.
The Kirby method sounds excellent. It should really improve operation of the layout and the overall appearance/effect, especially if I were to ever demonstrate this to folks, possibly at a model railway show, etc.
Cheers, Rob