Proportioning valve question

This is from 67 FSM ( the proportion is close to 65%)

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69 FSM ( the proportion is closer to 75 %)
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73 the combo valve has the same spec as the pre 73 separate valves but the combo "metering" valve is a bit different in function

Though I don't think they were used on A bodies.

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I'm impressed with your knowledge and ability to produce the documentation on such short notice. It's exactly as you indicated. Thanks for the lesson. Just to let you know how uninformed many people are. Was talking to gentlemen at Accurate Exhaust today. He said distribution block was a proportioning valve due to presence of dual master cylinder. Best he stick with exhaust.