[Dick]

I agree with Charlie on this....probably a very large project.
You will have to modify the center cross section of the frame to accept the C4. Not sure but may have to create a new trans cover; floor modification. Then build a mount for the new trans. Convert to open drive or modify the trans to mate with the torque tube in the '41. figure out a shifting system or use a floor shift. Using the flat-o-matic you can stick with 6 volts, original starter and probably not have to modify the fire wall.
You will need a transmission cooler as well. I'm probably forgetting a few things.