I'm running a 125 shot of Nitrous Works on my stock 90 GT.
Here's what I did:
-MSD Window Switch off ebay turns nitrous on at 3000 cuts it out at 6000 just in case I miss a gear
-Definately need a bottle pressure gauge just in case you don't have one allready pressure to nitrous is key
-NOS bottle warmer, not a must if it's always warm where you are but the first day I took mine to the track the bottle was to cold to get pressure, 500 PSI, and it ran like $hit
-I'm running 12 degrees of timing with Autollight 24 plugs gapped at .035 and have absolutlely no problem with detonation, only change to factory ignition is a set of Accell Wires and an MSD coil(coil might help I allready had one, you need a strong enough ignition so the nitrous doesn't blow out the spark)
-I made a button setup for my ashtray kind of like the painless wiring one they're selling for mustangs now, two lighted switches one for bottle heater one for arming, the lights really help at night
-Make sure to replace you're fuel filter just in case you don't want to run out of fuel.
Stuff that would be nice
-Fuel pressure gauge would be nice, I'm working on trying to find an electronic one to put inside that I can actually afford
-Purge valve, I've got one but can't find a good way to mount it and stuff with my kit so I've left it off for now, it's pretty much for consistancy from what I've been told, that and it looks cool
-MSD box, I wouldn't worry about a retard function those boxes are expensive. I'd just get a normal 6AL and you should be able to run the same timing as me if you've got enough fuel.
I've yet to have a chance to actually make a pass on the 125 shot but I made a bunch of passes on an 80 shot my quickest being 13 flat on cheater slicks and the 125 seems to pull twice as hard as the 80. It's fun to hit the button, I was nervous the first time but now it's no big deal. You'll be fine, most of the horror stories about nitrous seem to be coming from people who are doing crazy stuff.