68 K10 Brake Question

[Dave K.]

Drums all the way around, no power. I installed new wheel cylinders and master but didn't replace the distribution valve (I believe this set-up had one of these and not a proportioning valve correct?).

So I went to bleed the brakes and I'm getting nothing out of the rear lines so assuming the distribution valve is seized up. I looked on Napa and couldn't find anything that jumped out as the same.

Any ideas on the correct part and source? Am I interpreting the lack of fluid to the rear correctly? When I can crack the line at the valve I'll probably know more but right now it's a bear to free up and I don't want to have to run a new one if I can keep it original (read trying to minimize the inputs here right now and the lines are as noted externally very solid!).