Soft brakes after rear disc install

I think you mean that only 1 front tube will exit the proportioning valve, in which case, you should block the other front output port (FO). Autozone carries SAE inverted flare plugs in bubble packs (or did). Presumably, a downstream tee goes to both front brakes. Perhaps what you mean by "drum-drum distribution block". The rear tubing shouldn't go to that block, and only connect to the "RO" port.

The switch at top of photo is a "pressure imbalance switch" which will light the "brake" dash lamp (none in my early-A's but added a lamp). It grounds to light the lamp, which you can parallel to other brake switches which ground as a warning (e-brake on, MC reservoir low). If the imbalance switch trips with no pressure on the brake pedal, you might need to crack some ports to relieve pressure to re-center it. At least I've read that for the factory switch, though seems unnecessary since it should measure FI and RI pressures which should be open to the reservoir (fill ports open) with MC piston retracted, but someone might explain why not.