A Body Disc Brake help

Let's look again before we decide just how much suspension we will move.
Your 68 K member will be almost fully boxed underneath. If you have a sway bar it will route around that K member.
Now look at the later model. If that K member has huge cutaways underneath where a sway bar would route through it... Get it all including the steering gear and transplant all of it into the 68 whether the sway bar is actually there or not.