The stock water pump in my 87' went out on me about 2 months ago and I decided to change it, no biggie, at least untill 2 of the water pump studs broke off inside the block so I had to pull the timing chain cover off to get to the bolts. My Mustang had 144K on now while there was no huge deflection in the chain it was still out of spec so I changed it. The only thing I noticed was a bit better gas MPG.
Best insurence you can get once you have that many miles or KM's on a vehicle that your timing is proper and in the worse case you don't break one and smash a bunch of valves.
One way to check the chain to see if its really out of whack (a good check if u want to no without tearing it apart) take off the distributor cap, turn the engine over one way, note the spot of where the rotors pointing, turn over the engine the opposite direction and notice how long it takes for the rotor to move again, Ive never done it but my voc teacher told me about it. And I would throw in a new timing chain set in there if youre in there.