You don't need platinums, but they'll last longer. GM replacements are about 7-8 bucks apiece. NGK-TR55's are about $2.50, and should last 15-20k miles. They should be gapped at .035, otherwise you could have some mis-firing. They'll out-perform platinums, and will be fine as long as you don't mind changing plugs more often.
You'll have to drop the Y-pipe in the car to get to the #6 and #8 plugs. You won't want to, and you'll try to change them without doing this, but TRUST ME...it's soooo much easier. Be prepared to fix any broken studs when you drop the Y...I just drilled out the broken ends, and put a nut-and-bolt in. The #2 cylinder will be the hardest, because you don't have much room to work. Make sure it isn't cross-threaded!
Don't forget the anti-seize on the plug threads either. Hope something here helps [img]/infopop/emoticons/icon_smile.gif[/img]