Proportioning valve

That is where I get a bit confused.... I had read that it was in 71 they went to an actual dist/prop valve singular instead of the two piece (dist block/safety and the prop valve) you are talking about.

My car still had all original lines, or at least they looked original bend quality and enough crust to lead me to believe that, and was nothing else in the rear line. It was plumbed directly into the big block without the secondary smaller prop valve.