There’s some info on the process on a thread I started a couple of years ago. I still haven’t worked up the enthusiasm to undertake the job! Still, I can manage well enough without the heater, so I just cut the heater matrix out if the cooling water circuit.
I would genuinely be interested to hear how you get on should you proceed with the task.
http://www.lancia.myzen.co.uk/forum/index.php?topic=12653.msg90771#msg90771