The connections to your proportioning valve are going to be 3/8”-24 in and out. Here is a pic I made myself two years ago so I knew which fittings to get, to get rid of my factory combination valve and re do all the lines and just run a single proportioning valve to control the rear brakes. Don’t pay attention to the crisscrossing of the lines shown on top. That is for my own use, as I am using a corvette style master cylinder that has the rear brake reservoir at the rear and front at the front. I had to criss croos because our factory MC is rear brake reservoir in the front. What you are concerned about are fitting sizes, so this should be a big help.

I wanted to add, also, that if you try to find off the shelf 6” lines at your local Orileys, NAPA, etc that have the fitting sizes already at the ends like what’s on our trucks, good luck. Our factory lines are 3/16”, and to try and find a 3/16” line with 1/2”-20 on each side will be no where to be found, or you get lucky. The lines will be in 1/4” tubing with those size fittings. It’s best to source the fittings you need, then just re flare new ends on the tubing. Another option is to get 3/8”-24 fittings at each end of 3/16” tubing, and then get adapters.

I have have all sorts of fittings and adapters, as I am prepared to either do adapters or just re flare new fittings on. I’m actually going to start all of this as soon as I get home, but hurricane Lane has got me stranded till the weather clears, lol.

Mark, the criss cross job I did was somewhat of an emergency when I did it. I remember driving to Orileys(in another car, not the dodge) to try and find 8” lines with 1/2-20 at the end of one line and another line hoping to find with a 9/16”-18. Did not find any that came in a 3/16” line. I had no special tools for brake line work at the time, and needed 3/16” lines cause I know those can easily be formed by hand. So, I ended up buying the 3/16” ones with the 3/16”-24 brake fittings at each end, knowing I could make it work cause I had adapters to mount onto the master cylinder and another set for at the combo valve. The 1/2”-20 and the 9/16”-18 adapters threaded in easily into that Chevy cylinder, so I know the sizes I called out are correct. Maybe you had an odd ball one?

Mhuppertz, so what did you end up doing? Are you just going to strictly run just an adjustable proportioning valve to tame the rear brakes, and get rid of the factory combo valve, or are you using both the adjustable valve with the combo valve? Curious as to how yours works out.