Could you post a pic of the master cylinder where the brake pipes exit the body of the master...
Disc/Drum pipe sizes are different where they exit...disc system (front port) is a larger fitting...and pipe.
The proportioning valve is usually mounted a little off center, with the front of the block pointing towards the fan more...
The wire fitting is for the Brake Fail system...I suspect you have been bleeding the master as there is brake fluid around the rear port fitting...or is it leaking?
One thing to remember, when bleeding a system, you should remove the brake trip switch totally, to allow the shuttle to return to center as you bleed the system...once done...replace the switch and wire...
Now, I believe, some late 71 on-wards had the valve and block under the radiator cross member...maybe someone has replaced the valve with an earlier model system...check under the front cross member for the wire...not the suspension cross, the smaller one between the radiator support and the suspension...
