I ended up taking the radiator off, which turned out not to be nearly as bad as I had feared.
The new sensor is in and....
drum roll please
The fan comes on automatically!!!
Yay finally!!
It comes on at a slightly higher temp than I expected, just a shade over the 3/4 mark and stays on until just about bang on 1/2 way point, does that seem about right?
I also installed new sparks plugs and new HE leads. All the brake work is done (new pistons, new seals, new EBC pads etc), tomorrow I plan to do a quick throttle body balance before taking the missus to Volcano Arenal at the weekend.