I was just thinkin' about the transmission. Surfin' around, I found an adapter for the 392 to a Chrysler A904 (small block transmission) for the ridiculously low price of $475.
http://www.riley-auto.com/ADAPTERS.html
If this were my project, I would take into consideration the total cost involved in getting the drivetrain into place. The C6 might be free, but if you can't find an adapter for it, then it is a moot point. And if you do find an adapter and it's $1000., then that isn't a good plan either.
Rescue an A904 from a boneyard and have it rebuilt or score a rebuilt unit if you trust the builder. I'm just thinkin' that an all-Mopar drivetrain would be neat.
This is just with some quickie surfing, there may be even better deals out there with another type of transmission.