Dale, do the K-line trucks have a flat bolster joining the sideframes together? If they have a raised section like MTH or Atlas, yes - replace them with Atlas trucks. Anyway, those K-line trucks are a twin coil-spring freight car type. The Atlas caboose trucks with leaf springs come in 2 types - friction bearing or roller-bearing journals. Choose the one you prefer for the era you're modelling.
I asked about bolsters above. If the bolsters are 'flat', regular 2-rail trucks should work, trouble is I don't know what is currently available for cabooses - anybody know? If I had to do it now I'd probably replace the coil springs in a freight car truck with Pecos River p/b leaf springs which I have in an old, dusty bag. Yup, they're no longer made.
When you've sorted out the trucks(!), get the Kadees on and look at some good pics of the caboose ends to see if adding a bit of end-sill detail would put a smile back on your face 
. Oh and let us know how you did, it's got a good superstructure!
Jason
