kp60 = 2k
kp62 = 3k
kp61 = 4k
(callum said so)

more often than not the kp61's have a U series 6" head and larger splined axles but in your case it's not so. the other kp's often have an X series 5.6" so a good chance of interchangeability. if you swap head size you'll have to swap matching axles too.
imo, i prefer to swap just the head. i dont like disconnecting the brakes requiring to rebleed em, or handbrake cables etc. timewise its likely quicker changing whole lot. i like to check a new diff head before it goes in and do oil change etc, check seals and fix any leaks... for the sake of reliability. and at least i know the brakes are in good working condition.
you shouldnt need to pull the brakes apart at all to take the axles out. the axle retaining plates are able to twist past the brakes without removing anything.