The alternator-crankshaft pulley alignment doesn't look all that bad in your pictures.

A better way to check alignment is with the belt installed and under normal tension then placing a straight edge across the face of the pulley with the far end at the crank pulley. You can do the same from the crank pulley back to the alt pulley, needing to measure for equal offset from the straight edge to determine alignment. The alternator pulley is a fairly long span and as long as the straight edge ends up within, say, about 1/4" of alignment at the crank pulley when installed and tensioned then I wouldn't expect failure in 10K unless you're operating in severe conditions.

When belts are tensioned the alignment changes slightly, especially when the rubber mounting bushings are getting older, but also due to minor freeplay in the assemblies. When it's just pulleys a bit too much out of alignment, it's more commonly a matter of noise, squealing, belt glazing and signs of premature wear before a catastrophic failure happens.

o It would help if you posted the make and exact size marking of the belt you used, also how long it was installed for that 10K.
o Take your broken belt and folding it backwards fairly tightly in a number of places, is there much sign of cracking?
o Was it making any noise during running prior to failure?
o Did it fail with a separation at the belt joint seam and frayed ends there or elsewhere along the belt?
o Especially, please try to describe how you determine the belt tension. If you use the finger deflection method, try to describe how hard you are trying to press and how your fingers are held. If you use the twist method, how far were you able to twist it between the tips of your finger and thumb?
o Was the belt tension similar to that of the A/C compressor belt? Similar to that of the PS pump?
o Was the belt at all fluttering in use?
o If you lay the broken belt in the alt pulley and press down, does the surface ride dead even, above or below the outer edge of the pulley?

My best guess at this moment would be an inferior belt, an incorrect belt size, an over-tensioned belt, and much lower down the list something unusual happening at the pulleys.

If the belt size is correct and you're not over-tensioning, I would be very tempted to think the first belt might be faulty and to put on another belt and see if it happens again. You could spend hours trying to get all the pulleys into better alignment and for no great purpose other than your satisfaction if it was just a faulty belt.

I'll mention that for years now I've been using a proper belt gauge (Krikit) using different specs for new and used belts and based on belt width, not span. Takes all the guesswork out of it and helps keep my belts stay quieter for longer.

And you're right, Volvo accessory pulleys are often not in perfect alignment with the crank pulley and those rubber accessory mounting bushings don't at all help. Eventually the mounting holes wear a bit and the bushing are a lot easier to pop in and out. Worse still, there is no easy method of correcting for this other than removing the entire mounting bracket and elongating slots or shimming behind at the block. Way back, I once shimmed between the alternator mounting bracket and the block in order to improve alignment, but won't be trying that again anytime soon, not worth the effort as I had to remove it a couple of times as I kept dropping fasteners down in behind, the second time there was nothing behind, it had rolled way down the garage.

If you think alternator pulley alignment is a pain, wait till you try checking the A/C compressor pulley. Keeping that pulley in perfect alignment after tensioning is a bit of an art. It can become a trial and error process of tightening the rear adjuster bracket bolt first then adjusting it tighter to force the front out a bit to achieve alignmemt, then tightening the front bolt. If you get too carried away you can easily break the long 10 mm adjusting bolt. Using a pry bar can help take the strain of the adjuster bolt, also backing the bolt tension off a bit after the A/C compressor is locked in place.

I can't remember you saying where your non-North American '97 940 came from before finding its way to NS. I figure people have to really love their cars to transport them across oceans.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now