I'm not into flaring ;)
I got rid of my rear bias valve, just running a single line from the front proportioning valve to the rear rubber brake line. I used a XJ proportioning valve rather than block off the 2nd rear line. Why? Because I had one on hand.
Running an XJ prop. valve, or capping the 2nd line on the MJ prop. valve, are both safe. It basically makes it the same setup as the XJ. All that second line is good for is adding fluid for the rear bias valve.