Dual Master Cylinder brake lines?

It helped a little bit by getting those tubes and block. Slightly easier than adapting what is on your car.

Did the 70 donor have front drum brakes? If so, the junction block is just a distribution block w/ imbalance sensor, without the integral proprotioning valve. It looks like that, but search for photos on FABO. If I am right, you will need a separate proportioning valve in series with the rear brake tube and downstream of the imbalance block (if you will use the warning light).

If the donor car has front disks, go back right away and grab all the front disk parts including the spindles, since worth ~$200 used. I doubt it since a slant six. We could tell if the MC wasn't missing.