One side lifts but other does not

Your town car probably has an Air Bag Type suspension ... it sounds like either your air bag on the sagging side is leaking, or the air line going to it is not doing its job...There are shock and spring retro fit kits out there to replace the air bags fairly cheap...hope this helps

Spot on dockg! A Spring and shock kit works very well but the vehicle will lose the ability to level itself when loaded with a large cargo or several people. Most of the time, that isn't a concern.

I put Strutmasters all around - rides just fine, came with beefier rear springs and load capacity is fine too.

Are installing conversion kits difficult? What tools would I need to do so?

Generally speaking, unbolt the rear shocks and let the 3rd member down far enough to allow the Springs to come out. Just be careful whenever working under a supported vehicle.

Also be careful cause the springs( themslves) can kill ya.I did watch a promotioal video (all be it ,it was their own) after I heard about conversion kits. They made it look pretty simple (again - they are trying to make a sale) but I asked around also and as it turned out it was damn simple[ except for working with existing rusted bits] but that's to be expected.