Here is some hopefully helpful info. I rebuilt my proportioning valve (been thru this stuff with 2 cars - a 71 & the other a 69), and I would say one thing that may have been missed above is that the plastic sensor switch that is in the prop valve should not be exposed to fluid. If fluid is coming out of the sensor switch, this means that there is a fixable, but internal leak in the prop valve.
There is a "shuttle valve" inside that moves back and forth if the front & rear hydraulic chambers are not producing balanced hydraulic pressure (note that bleeding brakes and not using a centering tool will also move the shuttle valve to one side). This shuttle valve has seals that should prevent fluid from entering the cavity where the switch is operating - even if one chamber has failed and the valve moves all the way to one side. So, if fluid is coming out of your switch, it's time to pull the prop valve, get a rebuild kit from musclecarresearch.com, and rebuild it. Most of these prop valves are completely rebuildable, and the kits are like $25 with great instructions. (Find out if your switch is good or not and if it comes with prop valve if you buy one because the sensor switches are like $25 each also)
I had a "hard luck day" rebuilding my prop valve which is documented here:
http://www.7173mustangs.com/thread-rear-brake-issues-don-t-let-this-happen-to-you
Maybe there is some help in that if you can get thru reading it all.
The other leaks you mention are probably from the new lines. Fortunately, you bought OEM steel & not stainless as stainless is hard to get seated properly (mentioned above), but since they are new you are likely facing issues that the flares aren't seating properly because they are new. Loosen and retighten, maybe several times, but don't overtighten, as you can damage the line and or the seat. I would inspect the flares for splits like mentioned above, as no amount of tightening will ever seal a split.
Good luck!