Hi there,

I can understand the reason why you wonder about a bolt on the bottom of the A/C if you have ever worked on the alternator's bushings. I replaced my bushings on the alternator with solid PVC plastic bar stock. I turned them to fit the aluminum holding bracket. That is after I made the holes round and in-line to each other by line boring them in a milling machine.
The rubber bushings are used to compensate for a lousy casting tolerance. The rubber gives in so many ways it's sad to see it "sloppy or slapped" together on what was a fairly expensive car when new, IMHO. Not Volvos finest engineering hour.

The A/C is not mounted the same way, so the answer is no, there is nothing you have to do from underneath unless you want to remove the compressor. It's solid down there. Nothing like rubber flanges for retaining shoulders.
You only have to loosen the front nut on the adjusting bracket and another on the rear end of the compressor ears. It is a little difficult to get to though, if you try to do everything with AMM and hose in the way.
It can be done with a box end wrench or a socket with an extension all the way from the front.
The trick to using either method is having the right lengths on the arrangements.
I have used a 3/8" drive set with a universal swivel right of the socket so it will lay flat enough to get on to the rear nut and get the extensions to couple up through the front bracket openings.

As far as the power steering belt goes you will alway have to adjust it last. This is because as the compressor moves in a tangent arc or part circle. The power steering unit moves in another opposite arc upward or outward movement from the arc below. This will always make the length vary. The drive sequence dictates it to be the last one.

The A/C belt should flex only about the thickness of the belt, midway between the pulleys. The squeal should only be heard with the A/C on. You may want to inspect the compressors bearing under the clutch plate for its to free spin by spinning the pulley while you have the belt free.
Also check the crankshaft harmonic balancer pulley for separation.
Paint a straight reference line across the face from the insides to the outside so you can keep an eye on it. Sometime or another you can have trouble with that pulley as it ages.

The winter time is the best time to work on the belts and A/C under your chosen conditions that Mother Natures.

Phil