spare? it is the coil bracket, Ive got a couple of them as well (from donor cars and such...
The only other "similar" bracket is the alternator bracket, which has a stud on one end instead of a hole... Those are the only two bar shaped brackets im aware of on the hot air cars.
This is the correct location for the bracket. Basically it braces the alternator bracket from the rear. Most people never re-install it after removing it.