Then you're aware that the 153 and 168 flywheels use different starters, correct?
Because they bolt up differently, most, but not all blocks are drilled for both starters. If your block wasn't drilled for both, then you will either need to switch to the other size of flywheel, etc..., or drill and tap the block so you can use the other starter.
If the problem is with the snout of the starter not fitting in the bellhousing, then you either need to use a different starter, or do some grinding on the bellhousing to make it fit. Have you tried to use the starter from the '89 Firebird?
