[Speedbumpauto]

Without looking at your hardware or talking to the CPP folks, I think there is confusion between tubing size and wrench size. The wrench size for the standard 3/16 line is 3/8. I have not seen a 9/16 flare nut for 3/16 but have seen factory heavy duty 1/2 wrench size 3/16 flare nuts. If the 9/16 wrench size is correct, I believe the rear line is 1/4 tube. I have seen hd flare nuts for 1/4 tube in 9/16 wrench size used by the factory. 1/4 tube would be an OK choice to run to the rear for both brakes if you can get the correct flexible line from the frame to the rear end. Then you could drop down to 3/16 on the individual lines to each side. Neat and simple. If it was me, I'd take my proportioning valve down to the local auto parts store and try fittings until I found the correct combo. Bet it will be simple. Hope all the fraction sizes make sense.