Anyone ever eliminate the prop valve?

Many have done exactly what you suggest. I did so on my 65 Dart and am working on that for my 64 Valiant. I used a later aluminum MC on both (w/ booster on Dart).

You may need to leave the T hanging, just supported by the tubes. Another option is to get the distribution block from a pre-68 car (like mine) and plug the R port to make a front T (as I did). However, why not just take out the guts of your proportioning valve per 67Dart273's photo above (spring and plug), then use your external adjustable valve. That will leave your warning switch. If so, you might want to mount it high so the prop valve is not down in the mud.