big block a body swap

Depends on what you want to do with the car. Old scho drag racers prefferred the 6cyl bars as they allow the front suspension to unload faster on launch. Most people nowadays seem to put in bigger bars for handling. Remeber that they are fully adjustable, you can set the ride height wherever you want.....

As for the k frame, no difference as long as you have proper mounts. Looms like the big blocm is already in there!