I have done it. I run chevy rear disks. I would not go back (I rarely adjust it, except when I am fully loaded), the valve is mounted in the cab. I used SUM-G3905.
I did the same thing as Rocksurfer but I definitely don't have as much rear brake as I would like.
I like that prop valve 4runnerchevy. Pretty reasonable. What did you do with the unused line?