Will a 2004 S 80 AT 2.9L transmission Fit my 2002 S 80 AT 2.9L for a full swap?

There are a lot of configurations for the S80. The engines vary as well as the transmissions.
The transmision came in 3 general flavors in the USA.
The TF-80SC, Twin Turbo and an All Wheel Drive version.

On the engine code, the 6 & 7 position numbers indicate with further detail on applications;

65 is the S80/V70 FWD 2.4L
72 is the S70/S80 TDi FWD 2.5L
85 is S8o AWD V8
97 is the S80 FWD 2.9L
98 is the XC90/S80/V70 5.2L
99 is the S80 T6 AWD 3.0L

And the gear ratios are different depending on the engine used.

So, there is a lot to consider when thinking of a straight swap.
A knowledgable transmision shop will be able to take your VIN number and match the correct S80 transmision for your engine.

I do not have any more information in regards to VIN identification and the corresponding transmission to give you an answer that I could say, "It will be a straight swap".

Not only are there issues with the cases being different, gear ratios being different, possibly mounts being different, there may be issues, and there will be with such a large group covering Twin Turbos and All Wheel Drives, with snensors and even if you can switch sensors on the transmission, the torque converters will not match up as they respond to different pressures for lock-upand the engine/transmision harness in the car will not match up to the sensors on the transmission in regards to the signals sent to the computer.

So, I would first suggest re-builing the trnsmission, there are links on this site for reputable transmion shops, you do not know the condition of the transmission you are getting despite the mileage.

In the least find a used transmission shop that understands how the VIN will indicate the correct transmission for your car and then match it up to the correct transmision codeon the transmission itself. If a shop does not ask you for your VIN number, they are not going to be a dealer that will assure you that you will get the correct transmission. They generally do not take returns and you will be stuck with a useless part.

Go on-line and research either re-builders or used dealers that have a good reputation. You can always find somethng in a blog for Volvo enthusiasts that will mention dealers that they had trouble with. Good dealers will possibly give you a warranty, it may be short, have a proffessional looking web site and be very knowledgeable and ask you for information such as VIN numbers.

The best thing to do would be to find a local transmission shop, maybe one that specializes in Volvos, which you can find through links in this site and have them re-build it. If any issues arise, you will have them to help you and not have to pay for shipping and removing and replacing the transmission, if you get a good warranty from an on-line re-builder, and the fluids for a transmission cost a lot becasue they hold 10+ quarts.

To avoid a money pit and avoid spending far more than you may save on the risk of the swap, research at least the transmision you have. Ask a transmision shop for the codes to look for on the transmission to ensure it will be a straight forward swap/ This is the only way to make sure that you won't get into a situation where the answer to your question is, "They will swap if the transmision codes are in the correct groupd and only a good transmission shop will have that information". I would not even trust the information you may find on the internet.

I hope this helps and I gave you the information you need to make an educated decision and weigh the risks as well as have a way to confirm that what you have will swap out without issues.

If you have any questions, I will be here. Even though I am tapped out on information I can still answer questions about the information I gave you and please do feel free to come back and ask me to clarify anything that you have any doubts about.