The worst part is the lack of space. I have not done a 406, but several 405s
and 205s. As long as you have the Haynes manual covering the diesel engine,
you should have no problems. Assuming that it has the same spring loaded
tensioner arm, then as long as you follow the instructions you will end up
with about the correct tension. The other type, where they talk of hanging
weights on levers to get the tension is more difficult, and you may want to
get the tension properly checked when it is finished. As already mentioned,
you might want to change the water pump too, as for the £15 or so that it
costs, they are a b***** to do at any other time.
You will find that removing the crankshaft pulley bolt is difficult. They
use locktite. Engage 5th gear and either get a colleague to put their foot
hard on the brake pedal or you might be able to put a heavy screwdriver in
the slots in the dusk and wedge it against the brake calliper, then use a
long bar on a socket.
You will also need 3 x 8mm bolts to lock the belt timing, and a bit of 8mm
rod, or a drill bit, to lock the flywheel. A bit of stiff wire wound round
this rod will help to fit it and retrieve it later. You wil need a torch to
find the hole behind the starter motor.
Good luck,
Brian.