Hello,
That probably won't work, the KRC4 motor drivers use EtherCAT for communication and look very different from that older unit.
So before you buy anything, check with KUKA support if a given part is compatible with your controller.
We once had KUKA retrofit a 7th axis on a KRC4 and it was quite an evolved process that took a while.
I think - but might be wrong - that we paid 7k EUR for the hardware including installation (but excluding a motor), though even that might have been a special academic pricing.
Best,
Johannes