Your posting wasnt clear regarding the problem but I will take a guess as to what you are finding:

The serpentine system is an aftermarket item. Your engine is a real Chevrolet engine....the heads are vortec style heads.

As I remember, the vortecs have the accessory holes tapped with a metric thread and the pattern is slightly different than older heads. Have you verifed the thread style on the bolts in your kit? I'll bet that the bolts are 3/8-16 and the heads are tapped 10mm. Also, you should make a pattern of the pattern on the heads and compare it to the pattern on the brackets....I'll bet that they are different.....

mike in tucson