Upgrade a 401 heating system?

[Geoff Kingston]

In a few weeks time I will be stripping out the heat exchangers blower and pipework for the cabin heater and screen demister and am thinking now is the time to think about improved demisting and better heating.
Any thoughts and suggestions would be most welcome either to improve what is there or to modify the whole set up with a more powerful modern under dash unit such as those sold by Holden's or Car Builder Solutions.
The car when it does get back on the road will be kept in use during the winter and our wet Welsh summers! so good demisting is going to be as important as a decent heater.
Geoff.