I thought i'd post a short video on how to replace the spark plugs in a 2001 S80 2.9.
Personally i recommend to only use the multi-prong Volvo plugs as single electrode plugs run didn't work well for me. During the first 10-15 seconds after starting when very cold the car would run rough, seems better with the multi-prong ones. I'm guessing Volvo used these for a reason.
I'm guessing opinions will start a holy war, but that's been my experience.
Replace spark plugs in a 2001 Volvo S80 - How to - YouTube