All good suggestions from others...lots of very knowledgeable folk here....
I suspect the proportioning valve has sensed the bleed process, tripped over and blocked off the rear brake circuit...
Did you use the tool to stop the prop valve from tripping over? Like
https://www.classicindustries.com/pr...2.html#reviews
If the rear hard line before the flex hose has little to no pressure, the prop valve has tripped over...
Remove all switches from the prop valve and master cylinder and jump on the brake pedal once real hard...the trip valve will usually reset itself.
Also, try bleeding the system using a pressure bleed canister tool with and adapter to fit the top of the master cyl...
Constantly pushing the pedal only aerates the fluid and causes more issues.
Finally...hope you are not using DOT 5 fluid...its is silicon based and not suited to most aftermarket systems...stick with DOT 3 or DOT 4....