Thanks for the help Texan. That info helped me get the job done besides being worried that I was missing something. I used the scissor jack like you recommended, although I positioned it at a different location (pictured) and also used a jack from the bottom. After getting the rear struts in, I tested them by standing on the back bumper and jumping up and down. They didn't bottom out like I was fearing they would, which gave me a lot of relief. After that, the front struts went in without any jacks or substantial effort on my part. The biggest remaining issue was the alignment, especially on the front axle where camber was so excessive that you could see the tilt in the tire.
The real test for me was getting the alignment done. I was worried that they would come back and tell me they couldn't do it because larger struts were preventing them from making proper adjustments. However they were able to perform the alignment without issue, apparently. There's a couple values in my alignment datasheet (attached) which were out of spec, and I might call them tomorrow to ask about that, but everything seems good so far. Possibly a tiny bit of wobble in the steering wheel around 45ish miles an hour, and it might drag a tiny bit to the right, but it doesn't seem noticeably different from before I changed my tires a month ago and is otherwise a complete success. I even had time to install the new cat while I was at it yesterday evening, which shouldn't be scraping the ground so much with the extra 2-3 inches I've gained. It seems to be more than just the height difference between the old and new struts, possibly because Outback struts are stiffer but also because I went with Monroe quick struts which are reportedly stiffer than the OEM style KYBs.
With this lift, the winter tires, the countless dents and missing trim strips, I think my Subaru might officially be a trashwagon. Well, I might need a brush guard to make it official, but it definitely is on the way! I've attached additional photos so you can see the results. Confirmed: You can straight swap the struts on a 2000 Legacy with Outback struts and no additional parts, and I am guessing that is true for the entire 2000-2004 generation. I'll let you know if I develop any problems down the road. If anyone can offer an opinion on the slightly imperfect results of the alignment, I'm all ears.