Couple questions before I do my brakes

Yes, you can put the prop valve under the MC. Many after-market kits do that. I did that on my Dart & Valiant, which both have a 2-bolt MC. I took a bracket off the MC of an Intrepid, which works great as a mount. I used the same adj prop valve - one w/ Jegs logo, one generic, but both appear from same Chinese factory.

However, one kink is that you have the pressure-imbalance switch in your distribution block, which my early-A's don't have. If you want that to stay active, you must plumb the prop valve downstream of it, which puts it "down in the mud". The after-market kits use a "combination valve" as in post #2. Of course, you could move your dist. block up higher, but starts getting Rube-Goldbergish. A new combo valve is ~$75 (In-line Brakes and others) and would be much cleaner plumbing, though you must rework some lower tubes.

BTW, many have wondered why they loop the factory brake tubes. I didn't on my cars. Some say "vibration tolerance", but they don't loop them elsewhere. Perhaps it was to give extra tubing for when the tubes twist off during an MC replacement, but the factory isn't usually so thoughtful. Perhaps it made an easier install or less inventory (one size fits all, coil the extra length). I did read that the wrapped wire under the frame rails was apparently so the factory guys could bend the tube by hand without kinking, but could have been also for debris protection. Some things become mysteries as the original designers die off. Often the answer is, "because we always did so".