As I recall, you need to fabricate a bolster for the K-Line cabooses. You didn't say which model it is, but the Atlas Caboose trucks should work fine as you can shave the mount down a bit if you have to. If it's an older woodsided model, the MTH wood beam trucks should work for you. They're designed to mount to MTH cars which don't have conventional bolsters and might work under a K-line car.
Hope this helps.
