'73 up brake distribution block/proportioning valve question

Thank you and I do agree, especially going to 12" discs but thought the point about the Master was quite surprising. I'll tell you mine IS the original as I have owned the car since 1974, so... coming up on 52 years old. So all lines and wiring remain the same then, with changing the distribution block to a metering valve? I got some kind of a factory metering valve a while back from a member (attached) but it in NO way adapts. It binds in a distorted angle and and will NOT seat flat using the original bolt hole/frame setup. I'm thinking it is for a B or E body? Again, thanks so much for all the knowledge here; this site Rocks!