I'm getting a loud knocking from what I'm assuming is the flywheel. If spun it around couldn't see any obvious warping, looked for cracks and I wasn't able to find any. Since the bellhousing blocks the bolts I can't really access those or check them. Are there any other possibilities or do I need to drop the transmission. This is on an 80s sbc 350 in my 81 firebird.

 

How are you looking at the flywheel, through the dust cover underneath? Besides chocking the wheels, put it in nuetral with the dust cover off, turn the flywheel see or hear if it is knocking.