1971 el camino durm to disc is porportioning valve change necessary

There are 2 forms on this site (further down the page) that deal with brakes. One of them is dedicated to brake conversions.

http://www.chevelles.com/forums/forumdisplay.php?f=16
If your question is about changing from a distribution block to a combination valve or proportioning valve, the answer is: Yes you need to change it or your rear brakes will lock prematurely.
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thanks for the info donor car had proportioning valve it was a 72 had to get new hoses and banjo bolts.
again thanks will probably start on next week