Well, I finished it up today but it didn't go without problems. Anyone picking up this thread from this post should bear in mind this is a 1999 S80, 2.9 non turbo with the hydraulic style belt tensioner, and Variable Valve Timing (VVT) on the intake cam.

First, just to note, I mentioned above and have read others that stated the belt can be slipped off (on a mechanical tensioner type car) without removing the aux belt pulley. Well, if it can be done, it looks like it would be pretty hard. Also as mentioned, you must remove it on the hydraulic tensioner style system so you can get to the bottom tensioner bolt.

The tensioner pulley is held on with a T45 torx screw. There was not enough room between the screw and the chassis to fit the torx bit on a ratchet. I tried a small 3/8" breaker handle and it too did not have a low enough profile to get on the screw. I ended up having to pop out the bit, grind it down by about a 1/16" and put back in along with the small breaker handle. It was still very tight, but it worked. Needless to say, I couldn't torque that particular screw when I reinstalled it.

If you put on a new idler pulley there is a new screw that must be used as this part has been redesigned.

When I went to mount my homemade crank holding tool (in the bolt holes for the aux belt pulley) I found that one of the holes was really difficult to thread. Sure enough it was slightly cross threaded. so I got tap and proceeded to chase it. It's an open hole and when my tap came out the other end I had badly marred the new belt! Off to the dealer to get a new belt. It was $60 at the Volvo dealer, my other one was $35 from FCP Groton.
It was kind of a blessing in disguise. The first one was a Continental (Contitech) which was stated as OEM. But I noticed the outer layer on the Volvo belt (both the original one on the car and the new one) was twice as thick as the Continental belt. I feel better with the heavier duty belt.

I put the new belt on which meant I had to remove the new tensioner I just put on. I used a large clamp to compress it. Be aware that it compresses VERY slowly. Don't try to force it! Crank down on the clamp until it's tight, then in a minute clamp a little more and so on until it's finally compressed. You can turn the casing until the hole lines up and then use the right size nail to pin it. I installed mine in the car with the nylon washer on it, the conically indented side goes up. There is no other orientation to the washer as it spins freely in place.

I put it all back together again. The VVT cam sprocket moves VERY easily and you must be careful to make sure it is still in the right place when you lay the belt. I made sure to count the teeth (cogs) in the belt between the intake cam mark and the exhaust cam mark (on mine it was 19 cogs including the cogs AT the marks). Sure enough the first time there was only 18 so I adjusted it a tooth on the intake cam gear. With the belt snug between the crank and the intake and the right amount of cogs between the two cams I pulled the pin from the tensioner again. A few revolutions by hand had no surprises. All good.

I put the aux pulley back on, and then the aux belt, then the crank nut and the damper. Then I finished installing the aux belt. Mistake! I struggled with the front timing cover for a 1/2 hour before I gave up and untensioned the aux belt. The spring loaded pulley is too far in the way when the belt is on. With the belt off and the tensioner pulley all the way to the right the cover went right on with no trouble.

All the details done it started right up and ran great. The valves sounded a little noisy right off, which was disturbing but that cleared up after a few minutes.

The last thing is a light colored plastic splash guard down by the front axle broke off (brittle from age and heat) that I'll need to replace.

Anyway that's about all I can post for the benefit of others who might need to do this job on a similar model or set-up. Hope it helps someone.