I installed H&R Super Sports on the Cobra before I took it to the body shop. Took me about four hours with a floor jack, two jack stands, a ratchet set and breaker bar. Then again, that was the fourth time I've installed lowering springs on a Mustang. It gets easier after a while.
I don't understand why you would get a nose up stance with Sportlines. I have Sportlines on my '02 and it sits slightly nose down. They've been on there for a little over two years, so maybe something's changed.
I'll give you some advice on your spring install...
The rears are the easiest to install. Just jack the rear of the car and put the stands under the frame rails. Unbolting the shocks and quad shocks will allow the rear end to fall low enough to remove the rear springs. They may come right out, or as was the case with my Cobra (not my GT, though), they required a bit of coaxing in the form of a long crow bar to come out. No big deal, though. The H&R's required a little coaxing to go in, but it wasn't too hard. Just use your brain and you'll be able to put the puzzle together no problem. Jack the rear back up, bolt up the shocks and quads, reinstall your wheels/tires, and you're done with the rear.
The front can be a bit more complicated. The Hayne's manual talks about and pictures a spring compressor that's supposed to work on a Mustang, but even Ford dealerships didn't know what I was talking about. But that's ok. You don't need a spring compressor. That's what the crow bar is for. You'll need it for the front springs as well.
Same drill for the front: jack the car and place the stands under the frame rails. Remove wheels/tires. Remove the brake calipers and tuck them behind the strut. There's a little shelf of sorts on top of the frame rail where you can set the calipers in such a way that they won't fall on you. That hurts. A lot. You'll need to remove the ABS sensor as well. A quarter inch socket will do the trick. Use an extension as well so you can work around the front strut. Once the sensor is removed you can unbolt the bracket for the ABS sensor from the strut and tuck the sensor and bracket behind the strut with the caliper. Now you can unbolt the strut from the spindle. You'll need a 13/16" and 15/16" socket. This is one place where the breaker bar comes in handy. These two nuts/bolts are usually pretty tight. Get the jack under the control arm in order to relieve tension on the strut to spindle bolts. Before you remove the bolts, however, go ahead and remove the nut on top of the sway bar. Once this is removed, go ahead and remove the strut to spindle bolts. Removing the tie rod is a pain and is not necessary; the control arm will be able to fall low enough to remove the spring with it attached. After all the above is completed you'll be able to lower the floor jack (slowly) to relieve almost all pressure on the stock spring. It'll require a bit of coaxing to be removed as well. Use some WD40 to remove the rubber isolator from the bottom coil of the stock spring. You'll be reusing this on your new springs. Don't forget the isolator at the top as well. That may be stuck to the K-member mount when you remove the stock spring. You're ready to install your new spring once you've installed the bottom isolator on the new spring. Take this opportunity to clean out the spring perch as it will be filled with debris.
You'll again need to use the crowbar to coax the new spring into place. Be sure you have a long one so you have plenty of leverage (that's what she said). You'll notice that the rubber isolator will resist going into the spring perch. If you force it into place it will likely roll over onto itself. This probably wouldn't be a problem, but you want to do this right. This little problem can be solved by dousing the perch (and the isolator for good measure) with some more WD40 so it will slide into place without rolling over onto itself. You'll see what I mean when you're at this point. Once the spring is in place you can go ahead and jack the control arm back up. Jack it with one hand while using the other to guide the control arm-to-sway bar rod into the hole in the sway bar. You can go ahead and install all nuts and bolts once you have the control arm where it needs to be. Repeat for the other side. Reinstall your calipers/ABS sensors, wheels/tires, get the car back on the ground, and admire your handywork.
It sounds like this is your first spring install, so I hope that helps.
. i have the notorious nose-up look 
. ironically, the car in the pic (my 95) has the same spring/suspension setup as my 2000. it sat level while my current car sits slightly up in the front 
(stupid eibach)
