2000 8.8 in a 96 GT

Funny thing. I just did this today. I took the rear end out of my v6 and ganked the 8.8 out of a 95 donor car. I had to put my rear end back into the 95 in order to make it roll around and after I put it all back together it worked fine. The 17x8 stock wheels/tires didn't rub. Keep in mind, I used my 2000's rear control arms as well.
 
You'll have to change the rear brake line setup. The 99+ rear has 2 separate lines running along the body directly to the rear calipers

the 94-98 rear end uses a single line running to a t-block in the center of the axles and then hard lines running out along the axle to solft line brackets on the rear.

You'll have to use the brackets from your original rear and then swap the brake lines over and extend them slightly.