cylinders 5,7,8 misfiring in 2000gt

alright, im posting this for my friend because hes having a problem. its misfiring cylinders 5,7, and 8. it will run fine sometimes and other it will just crap out. its hard to start most of the time and its cut off a few times on the road. the reason im posting this is because he just spent a bunch of money on a new hood and cobra bumper and is not thinking about getting rid of it because of this problem. any insight would be great because i dont know jack about the 4.6 motors. thanks guys

well we replaced his plugs trying to solve the problem and it worked for like 2 days. im thinking its bad coil packs. he had a friend pull the codes on it. he said it just said that those cylinders were misfiring. and its not 5,7,8 its 6,7,8. how much are new coil packs. hes not very mechanically inclined so he wont ever find the problem, but he knows some pretty smart guys that can. thanks for any suggestions