Have finally bitten the bullet and completed this job; took about an hour all in... Although I've already been through some of the work before to figure out the problem so knew how to get the resistor pack out.
I was lucky in that I managed to get the loom & resistor pack on
for £50 + £6 p+p
Anyway, it's a pretty easy job in the end.
Major worry was having to pull the resistor pack through so the red wires are long enough to access through the hole. I pulled with a firm force and I felt 2 points at which the wires extended. At that point I stopped as was worried about doing more damage and I had just enough access.
I've attached some pics to show what I did and the differences between the two looms/connectors.
Only tips I can give are:
. Disconnect the battery(!)
. Write down what connector goes onto which pin
. Double check your wiring
. Don't test the fan for more than a few seconds on each setting before reinstalling (resistor pack gets hot without airflow)
. Tie something onto the screwdriver you use to unscrew the resistor pack screws so you can retrieve it when you drop it behind the dash, which you probably will have to(!).
Thanks to all participants in this thread, it's been ever so useful.