One thing I have not seen mentioned yet is that the 454 is an externally balanced engine. What this means IF you end up swapping flywheels is that you will have to have one that is correctly balanced for a 454.

It's been along time since I did a 12" to 11" clutch swap, but it seems like the Flywheel would accept both. It seems like the flywheel needed to be changed when going from a 10.4 to 11" or 12"