I would replace the heater valve, heater hoses, and radiator if they have not been replaced. The upper and lower radiator hoses could stand to be replaced, too, but they are less likely to fail catastrophically than the heater hoses, heater valve, and radiator. If your car is normally aspirated, it probably has a B230FD engine, and Volvo gives the timing belt a service life of 100,000 miles on that engine. Replace the timing belt if it is close to that. I can replace one in an hour, and the part cost is less than $20 if you buy right.

If your car doesn't suffer a miss under full throttle the ignition system is okay, although preventative maintenance is a great idea.
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john