C6 is okay. Definitely tough but I've honestly wondered a lot about something Allison automatic. Surely there is something in the right SAE bolt pattern.
Just be a matter of figuring out the flex plate and converter. Then you could have lockup and overdrive.
Honestly, I'm not sure why no one figured out the lockup converter. Seems like an electrical lockup clutch wouldn't be all that crazy. It wouldn't have OD but you'd have a bullet proof core.