Updates on 2002 S80:

Thanks to all who offered their experience based on experience with this model.
"Cooling" the various vulnerable parts of the S80 has been addressed in various simple ways.
The underdash computers, clearly needing more air circulation, have been addressed by removing the lowest portions of the dashboard plastic trim--not visible by driver and passenger in normal seated positions--though the diagnostic port is now in clear view.
Under the hood, I removed the covers over the coils to allow better air circulation--a problem which turned up was the "looseness" of a cover over the camshaft belt, corrected by strapping the cover to spring clips used for the removed cover.
Finally, just as I did for the '81 245 Volvo, a "dryer vent" was placed on the passenger side hood allowing heat to escape, especially during the "heat soak" period after a trip. If painted and equipped with its Volvo insignia, it seems to belong.
Since there was some uncertainty about the condition of the transmission fluid, I sent a sample to Blackstone Labs in Indiana for analysis. Amazingly their analysis found the fluid (good, in this case!) with the same mileage as a record of maintenance I later turned up on this car.
Worn front end parts replaced, turn signal contacts cleaned and diagnostic port read via OBD Link SX--all systems go!