Wondering if anyone can help with info disc brake prop. valve.

The B-body combination valve includes a metering valve in the front line.
The A body combination valve without lines did not have a metering valve in the factroy system.
AFAIK the 'knee point' for both valves is the same, although the proportioning may be slightly different above the knee point.
The adjustable proportioning valve would be used with a distribution block (aka safety switch) that did not have the proportioning valve built in.

Look in the 1970 Hydraulic Brake booklet here for illustrations of the valves and what they do.
https://www.web.imperialclub.info/Repair/Lit/Master/
Also available in pdf format at www.mymopar.com -> Master Tech - > 1970