need suggestions on rear AC plastic housing
 

The rear AC blower on my '89 suburban has an upper and lower plastic housing. It was all cracked up from an old repair that a shop did and the blower rubs against the casing, making an awful noise.

So, I shelled out $105 for a new upper and lower piece and I still can't get it back together to where it doesn't rub. since the blower is just screwing into plastic, it doesn't really hold the blower very precisely.

Has anybody run into this? What did you do??