Disc brake upgrade questions

I wouldn't mount the adj prop valve down in the mud, though many do. Mine is right under the MC, as many brake kits do, but I don't have the pressure-imbalance switch in my early cars, so no "down & up" plumbing like you would have to do. I did keep my distribution block, which is just a 4-port "tee", but only the front tubes use it now. If you did use a later "combination valve", it probably won't be direct bolt-up and you might have to rework your tubes to fit, plus there is no adjustment.

I thought about installing an imbalance switch (like post #3), but would also have to add wiring for it. I expect it would give limited utility. When the MC in my 69 Dart failed long ago (pedal went to floor), it never lit the warning bulb. I expect the piston was rusted stuck, as in most cars. But, I didn't know about changing brake fluid regularly then. Today, I use silicone fluid so no more rust. Still, my new MC's have a reservoir level switch which will warn me if one circuit is leaking, which seems sufficient.