Look at FCP Groton for parts.

I like Roulunds (Ro-Drive) and Continental (Conti-Tech) timing belts. Both are good, if you only run them the recommended 50k, both will come out looking mostly new.

The aftermarket tensioners are fine. I usually replace them every 50 or 100k miles. Typically 50k, because they're $40 and getting towed is $100.

You might want to do a water pump as well since the job is so simple with the timing belt and covers removed. For the price, less than $40, the HEPU pump is every bit as good as the Volvo pump. I've used them time and time again, and they are the best.

And while you're at it, it might not hurt to order the three front seals either...
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1992 940 wagon, low miles
as well as others.