Cheers for all the replies everyone - it was an interesting read.
I found a bit of time today in a busy weekend to get the radiator etc swapped around. I'm really happy because the work went well and quite a few loose ends have been tied up with one relatively easy bit of spannering.
Here's the start of the work, with the undertray droped down, ready to get the bumper off - note the tape to protect the wing:
IMAG1610 on Flickr
Most of the panels removed and ready to go. You can see that the fan has a chunk missing from the accident that also wrote-off the intercooler and radiator:
IMAG1613 on Flickr
The old intercooler is obviously knackered - plenty of oil on the left as you look at it here:
IMAG1612 on Flickr
You can see here that I had double trouble - a leak on the Driver's side, and also the twist on the intercooler meant that it would never seal properly on the passenger side:
IMAG1611 on Flickr
Here's a pretty badly-taken picture of everything removed, ready to start reassembly with the new unit:
IMAG1614 on Flickr
I got new Condenser o-rings from DMGRS which arrived over night so it's been re-assenbled with those (I used the tiniest bit of 10w-40 to lubricate them) and also viton o-rings in the intercooler tube.
It's all back together now, except the bumper, because while I've got it off, I'm going to use a Turtle-wax headlight restoration kit to sort them out, too.
By the time it's complete, this bit of work (including the new rear bumper and bonnet) will have rectified:
-Dented bonnet with lacquer lifting replaced
-Dented and badly-repaired rear bumper replaced
-Parking sensors now work
-Cooling fan now works (resistor replaced)
-Replaced Coolant
-Intercooler not leaking
-AC Condensor replaced with new seals
-Wiring tidied up
-Headlights refurbished
-AC re-gassed
Not bad for a few hours work and about £300 in parts and service items.