Steering box interchange and more questions.

Will the box out of our 64 Plymouth fit my 71 dart?

The 64 is a non power box and that front end is going away so I'm wondering if it can replace the PS box in the 71 dart?

Also is the 64 BB K member swappable into my 71 dart?
I have a 318 K Member and wonder if the 426 BB K is better for my 440 than the 318 K?

What about the torsion bars? Do I want the BB bars? Will they fit the dart?

Thanks for all the help.