We should probably move this post over to the acoustic music forum, but for now....
Don't get too caught up in deadening your room just yet.... Upright pianos can sound pretty ugly all on their own. Sometimes the acoustic of the room will help, rather than hinder what you're trying to do.
For starters, you may want to move it out from the walls and have someone play it in the middle of the room; wander around and listen to it from all sides. You may want to take the front kickboard out as well...that sometimes helps, sometimes not. Experimenting is the key, and you'll want to get as much sound of that beast as you can.
No way should you use the SM-58 on a piano like that, unless you're stuck on a live gig with nothing else to use. (Hell, it happens, I know..been there, done that!) Check the sound coming out of the top with the lid open, certainly. You may want to try to put a stereo pair - cardioid, most probably - just above the opened top. (Avoid the temptation to stick a mic DOWN inside there, it'll pick up too much of any one key or groups of notes in that narrow opening....lopsided, over-exaggerated sounds will result.)
If you pull it out from the wall (assuming you're doing solo piano recordings?) you may find some good "Sweet-spots" around the back of the piano. (This is similar to the underneath of the soundboard in a concert grand piano, so it may sound more boxy and less detailed than you'd like.)
Again, you can remove the lower kickboard as well as the front (music rack) area of the piano above the keys, and mic it somewhat like a vertical Grand Piano, if you can imagine; try one on the top right (above the keys) and one on the lower left (by the pedals, below the keyboard). Remember, the big differences between grands and uprights are how the harp itself is positioned. Grands are flat - horizontal, uprights are vertical.
In the end, you may find a blend of the above mic positions will yield the best results. (You didn't say what genre of music you're doing, and/or if there will be other instruments playing along. That may influence the sound you're going for.)
I would think a pair of SP C3's will get you started if budget is a concern. They come with omni AND cardioid capsules, so you can experiment with that as well. The MXVV6 3M may prove to be too much of a good thing, as well....not sure if I'd want to record a piano with an LD Side adress cardioid mic, but hey if it works (esp on the soundboard area?), give it a shot!