Alternator removal question: I am replacing the.

Alternator removal question: I am replacing the alternator in a 1999 Buick Century. I have unplugged the electrical connections, and removed the bolts except one. The bolt I cannot remove is threaded through the front part of the alternator. It is attached to a bracket that is bolted to the engine block (I have removed the bracket nut and bolt). The bolt permits the alternator to move up and down. When I unscrewed the bolt it cannot be pulled out because the the head of the bolt (at it's extended length) butts against the plastic radiator overfill tank. There is no room to remove the bolt. Thus, I cannot remove the alternator until that bolt is removed. Do you have a suggestions to solve this problem?