Thanks again folks.
If someone could point me to the correct mc part # I would be very happy.
Most of the hits for 72 blazer MC, all the hits come back with the same 50/50 design. I see different options relating to drum/drum vs. disk/drum on the proportioning valve, however.
I did locate a few options at rock auto:
http://www.rockauto.com/catalog/x,ca...,parttype,1836
Oddly, of the three listed the raybestos is 50/50 while the others are 70/30 and none specify disk vs drum.
Leaning toward:
DORMAN Part # M71285 {First Stop #18008630, 3956521, 3979629, 406389, 5458528, 5463558, 5469489, 5472157, 5472650, 5472725}
w/Power Brakes; Bore = 1-1/8"; Moraine
As another data point, here's a power brake booster kit for 69-72 trucks. Again does not specify drum vs disk and is 50/50, but same site has proportioning valves that are specified to disk/disk or disk/drum:
http://estore.websitepros.com/126980...EVY/Detail.bok