The TD rad is a favourite for blocking with mud at the rear and looking clear from the front.... may be worth removing from the motor and the rear jetwashing out, The TD rad is a fair size, much bigger than the TDI which is why I have fitted one to my TDI and it runs very very cool in fact i have no fan fitted at all.
The rad may well be blocked and shot if old, reverse flush and see what comes out
As for fans get one off a vauxhall cavalier they shift a huge amount of air and the plastic surround fits perfectly top to bottom on a landy rad, it sits nicely in the bottom groove and a small bracket can be fabricated to attatch the top, used a few but got no pics.. sorry
As for a sensor I beleive x-Eng do a very good one that controls a fan but no doubt someone will be along with details
A final note... be very very careful letting a TD run in the slightest bit warm.. they really are crap engines if abused or not looked after carefully... hence the reason I now have a 200TDI..... I would rather go back to an NA diesel than a TD :)
Cheers Steve