Had the same problem with my partners Ka and I can confirm that it is a straight forward DIY job. As the part on back order I decided to effect a temporary repair.
Un-clip covers at base of wiper arms
Remove plastic covers from wiper spindle nuts with long nose pliers
Undo nuts on wiper spindle (13mm socket) and remove wiper arms
Undo the three plastic nuts (10mm socket) retaining the plastic shroud at base of windscreen
Remove rubber seal from front edge of shroud
Ease up the plastic shroud and disconnect washer jet
Carefully release corners of shroud from base of windscreen
Disconnect plug from wiper motor
Undo two linkage retaining bolts (10mm socket)
Disconnect loom from linkage
Carefully ease the motor and wiper linkage out taking care with the wiring for the heated screen.
That was it out, the linkage is made from plastic and metal and one of the plastic bits had sheared, So using Aradite precision I glued it back together, holding it together with tie wraps. Left it alone for 24 hrs and as they say in the Haynes manual reassembly is the reverse of the process.
Just want to stress, this is a temporary repair, we have a new linkage on order which I will fit.
By the way, as the Ford KA is derived from the new Fiat 500, and the Ford linkage is made in Italy, a Fiat 500 linkage may, I stress may, fit.