What is this all going into?
An '89 Firebird bellhousing would be the angled kind, and it is for the smaller 153 tooth flywheel and 10 1/2" clutch. The starter needs to be the kind with the bolt holes straight across, not staggered, IIRC...
With this bellhousing the rear mount will stay level. If you switch to a typical straight up bellhousing, you will need to customize the rear mount, just so you are aware of this.
As for not bolting up to your old cast iron bell, it should, unless it has the wrong center hole size. (I'm assuming your talking about one that will bolt up to a 292). If it has the larger 5 1/8" center hole, you could get an adapter ring from Advance Adapters that will take it down to 4 11/16".
No adapter plate between the trans and bell should ever be needed for what you are trying to do. You just need the right combo of parts.
