Ok so the bellhousing should line up without an adapter? My 305 had a flexplate that had 3 holes to be bolted onto the converter, so if the flexplate in a 396 doesn't have the right bolt pattern, will I be able to take the flexplate off of my 305 and use that instead?

 

They're all 3-bolt, all 120 degrees apart. The issue is that there were 2 different distances from the crank centerline out to the converter bolts.
The 396 is sure to have the larger version, while a 305 Camaro converter has the smaller one. You can't use the 305 flexplate because it has a 153-tooth gear for the starter, while big blocks must use 168-tooth. You'll have to stay 168 tooth because of the starter. If they don't match up, you have a few options, with the correct one being the most expensive. The "wrong" way involves drilling, washers, and longer bolts, while the correct way involves buying a new flexplate.

 

Dual pattern flex plate & 153//168 tooth starter?