1989 Firebird (Third Generation F-Body) will be too wide to fit the AD, according to most sources.
Most guys suggest the earlier ('70-'81) Camaro/Firebird rearend as they claim the width is right on.
I've got the second gen. rearend, but no truck yet, so I can't offer you first hand advice, Solo. I'm sure someone who's already done it will chime in here before too long.
Regards,
Wannabe
