Rob,
The vehicles in the photo are 12-wheelers, so definately not K cars. I can't see any matchboarding, but that may an artifact of over compression (I'm using a smartphone at the moment). However, K cars with some 6-wheel (US-sourced?) bogies may suit you very well.
If you find that the windows are the same as the K cars you may find out that Westdale can do you a special - it'd certainly be worth asking.
Oh and don't use Wayoh 6-wheel bogies, there's an error in the geometry of the brass inner and they're unstable; pretty much guaranteed to derail.
Steph